Envelope Blogs

The Number 10 Standard Envelope

The #10 envelope is the default business envelope in the United States. It measures 4-1/8 x 9-1/2 inches and holds a standard 8.5 x 11 sheet folded in thirds. It qualifies for First-Class letter postage when the contents weigh under 3.5 ounces, which covers most business letters.

For small businesses, the #10 is the right choice for outgoing correspondence, cover letters, appointment confirmations, contract follow-ups, thank-you letters, and any situation where a single folded document needs to reach a client or vendor. It is the format that recipients expect for professional business mail.

The standard #10 comes in several surface options. The white wove surface accepts laser and inkjet printing for return addresses and logos. The security-tinted version adds an interior pattern that blocks the document from showing through the envelope when held to light. The peel-and-seal version uses a pressure-sensitive strip that does not require moisture to close, which speeds sealing when processing multiple pieces at once.

See the full range of #10 envelopes in standard and specialty styles. For standard white wove correspondence, the #10 white wove printed envelope is the starting point.

Window Envelopes for Invoices and Statements

A window envelope has a clear poly-film cutout on the front face through which the recipient's address shows when the document inside is folded and positioned correctly. This eliminates the need to print or label the address on the envelope itself. For small businesses that mail invoices, billing statements, or account notices regularly, window envelopes reduce mailing labor and the risk of addressing errors.

The #10 window envelope (4-1/8 x 9-1/2 in) is the most common size for invoice mailings. Standard invoice templates in QuickBooks, FreshBooks, and most billing software are formatted so that the recipient's address falls in the window zone when the page is folded correctly. This means no alignment adjustment is needed in most cases.

Window envelopes are available in standard white wove and security-tinted versions. The security-tinted #10 window is the right choice for invoices that include account balances, statement details, or any information that should not be visible from outside the envelope. Closure options include gum flap and self-seal (flip-and-stick), depending on your mailing volume and workflow.

Browse window envelopes by size and style, or go directly to the #10 white window envelope for standard invoice use.

Double Window Envelopes for Checks and Bills

A double window envelope has two cutouts: one for the recipient's address and one for the sender's return address. Both addresses show through the envelope when the document inside is folded to the correct position. This format is designed for mailing checks and for billing statements where both the payer's and payee's addresses need to be visible without separate printing on the envelope face.

For small businesses that print checks or mail invoices with payment stubs, the double window format works with standard accounting software layouts. QuickBooks check templates, Quicken, and Sage print the check amount, memo, and both addresses in positions that align with the double window zones when folded. This means no envelope printing is needed for check mailings, which saves time on routine payroll and vendor payment runs.

Double window check envelopes include an interior security tint. The tint blocks check amounts, account numbers, and routing numbers from showing through the envelope body when the piece is held to light. The windows themselves remain clear to show the address blocks.

Three closure types are available: gum flap (moisten and seal), peel-and-seal (peel the liner and press), and flip-and-stick (fold the adhesive tab over). Flip-and-stick is the fastest for same-session sealing when processing a batch of checks or statements immediately after printing. Peel-and-seal is better for inventory that sits before use because the liner protects the adhesive during storage.

See double window envelopes for all formats, or go directly to the double window check envelope with flip-and-stick closure for check mailing use.

Security-Tinted Envelopes

A security-tinted envelope has a printed pattern on its inner surface that makes the document inside unreadable when the sealed envelope is held up to a light source. The tint covers the full interior except the window areas, where the address is meant to be seen. The security tint is an optical deterrent, not a physical barrier, but it prevents casual inspection through the envelope walls.

Small businesses use security-tinted envelopes for checks, payroll envelopes, financial statements, tax documents, medical records, and any mailing where the contents include sensitive numbers or identifiers. A standard white #10 envelope without tinting is transparent enough that check amounts and account numbers can sometimes be read through the envelope body when held to light. Security tinting removes that risk.

The 24 lb white wove stock used in the security-tinted envelopes on this site is heavier than 20 lb economy stock, which adds a second measure of opacity beyond the tint pattern. Both gum flap and peel-and-seal versions are available in the #10 security-tinted format, as well as the #9 size for tinted reply envelopes included with billing statements.

See the #10 security-tinted envelope with gum flap and the #10 security-tinted envelope with peel-and-seal for specifications and custom printing options.

Reply Envelopes

A reply envelope is a smaller envelope included inside an outgoing mailing so the recipient has a pre-addressed return piece. The standard reply envelope size is the #9, which measures 3-7/8 x 8-7/8 inches and fits inside a standard #10. When the recipient is ready to respond, they fold and insert their payment, form, or response card, seal the #9, and mail it back.

Small businesses use reply envelopes in billing and invoice packets, fundraising appeals, membership renewal notices, and any situation where the goal is to make responding as easy as possible. A colored reply envelope is easier to find in a pile of papers than a white one, which can blend with the letter and other enclosures. For that reason, businesses often use a colored or tinted reply envelope even when the outer mailing uses a standard white #10.

The #9 white wove envelope with gum flap is the standard reply format. A security-tinted #9 is the right choice when the reply envelope will carry a check or payment, so the amount is not visible through the envelope before it reaches you. Both plain and tinted #9 options are available with custom printing for your return address.

See the #9 white envelope for reply use and the #9 security-tinted reply envelope for options and custom printing.

Colored and Promotional Envelopes

Colored envelopes stand out in the mailbox before the recipient decides whether to open them. For small businesses running direct mail campaigns, seasonal promotions, event announcements, or any piece where open rate matters, a colored envelope is a practical tool. The color signals that the piece is different from routine correspondence, which raises the chance of it being opened before standard white mail.

Two colored envelope styles are available for small business use: wove (solid color, smooth finish, gum flap) and starburst (bold pattern across the face, peel-and-seal). Wove colored envelopes are the right choice for professional mailings where color adds distinction without a promotional look: color-coded billing runs, reply envelopes, or correspondence where visual sorting is the goal. Starburst envelopes are designed for direct mail campaigns where maximum visual impact is the priority.

Both styles come in sizes from the compact #6 3/4 up through the #10. For promotional pieces that need to hold a larger document or small catalog, the 6 x 9 and 9 x 12 starburst formats hold more without folding.

Browse the full range of colored envelopes by size, style, and color.

Large Format Envelopes for Documents and Catalogs

When the mailing contains a document that should arrive flat rather than folded, a large format envelope is the right choice. The 9 x 12 envelope (interior space 8.75 x 11.5 in) holds a standard 8.5 x 11 sheet with about 1/4 inch of clearance on each side, so the document arrives without fold creases. This matters for proposals, contracts, certificates, product sheets, and any document where presentation quality affects how the recipient perceives it.

The 6 x 9 booklet envelope is a mid-size option that opens on its long edge and holds a standard 8.5 x 11 sheet folded in half. It also holds a 5 x 7 card flat, a tri-fold brochure, or a small catalog. At 6 inches tall, it falls below the USPS letter-rate height limit of 6-1/8 inches, so light contents may qualify for First-Class letter postage rather than flat-mail rates.

For large format mailings where visual impact is part of the campaign, the 9 x 12 starburst and 6 x 9 starburst formats apply the same eye-catching pattern used on standard promotional envelopes to the larger sizes.

Self-Seal and Peel-and-Seal Options

The closure type on an envelope affects how fast you can seal a batch and how safely you can store pre-loaded inventory. Small businesses that handle mailing in-house, without a mailing machine, should choose a closure type based on their typical mailing volume and workflow.

A gum flap envelope uses moistenable adhesive. It is the lowest-cost closure type and works well for small, occasional mailings where moisture-activating the flap is not inconvenient. For larger batches, a sponge or water dish speeds the process.

A peel-and-seal envelope has a pressure-sensitive strip covered by a release liner. To seal, peel the liner and press the flap. No moisture is needed.

The liner keeps the adhesive stable through storage and shipping. This makes peel-and-seal the right choice for envelopes kept in inventory for weeks or months. It is available on most #10 standard, security-tinted, and window formats.

A flip-and-stick (self-seal) envelope has an exposed adhesive tab on the flap that folds over a matching panel on the envelope body. No liner to remove, which makes this the fastest closure for same-session sealing. The exposed adhesive is not designed for extended storage in open inventory boxes, so this closure works best when envelopes are sealed immediately after loading.

Self-seal envelopes are available for the standard #10 and window formats. Browse the self-seal envelope options to compare formats and quantities.

Custom Printing for Small Businesses

Custom-printed envelopes carry your business name, logo, and return address on the face, which reinforces your brand on every piece of mail you send. For small businesses, a printed return address removes the need for a separate address label on each envelope and gives outgoing mail a consistent professional look.

Custom printing is available on most envelope formats on this site. Key details to know before ordering:

• Formats available: #10 white wove, security-tinted #10, window formats, and colored wove and starburst formats
• Colors: Printing goes on the face in one or two colors
• Proof: A PDF proof is provided before production so you can confirm placement before the order ships
• Lead time: Blank stock ships same or next business day; custom printed orders ship 7 to 10 business days after proof approval
• Minimums: No minimum order, so you can print in the quantity your business actually uses

Blank stock (no logo or qeturn address) ships same or next business day. Custom printed orders ship 7 to 10 business days after proof approval. For small businesses that need envelopes quickly for a specific deadline, blank stock with a return address label or stamp is the faster option while a custom printed order is being produced.

There is no minimum order on this site, so custom printed envelopes are available in the quantities a small business actually uses rather than requiring a large minimum run. See the printed envelopes category for all custom printing options across formats.

How to Choose the Right Envelope for Each Task

Most small businesses need a small set of envelope formats, each assigned to a specific mailing task. Knowing which envelope type goes with which task makes ordering straightforward and keeps mailing workflows consistent.

For most small businesses, a practical starting kit is the #10 white wove for general correspondence, a #10 window for invoices, a double window check envelope for check payments, and a #9 reply for billing packets. Colored and large-format options can be added when a specific campaign or mailing type requires them.

Custom printing your return address and logo on these formats gives every piece of outgoing mail a consistent professional look without requiring additional labeling steps at the time of mailing.

Browse the full selection of #10 envelopes, window envelopes, and double window envelopes to find the right formats for your mailing needs.

Two Colored Envelope Styles: Wove and Starburst

Colored business envelopes come in two surface styles. Each has a different purpose and closure type.

A wove colored envelope has a smooth surface finished in a solid color. The wove finish matches standard white business envelopes: clean texture and compatible with most laser and inkjet printers for return addresses or logos. The wove style uses a gum flap closure. This is the right format for professional colored envelopes in office correspondence, reply pieces, or color-coded billing runs.

A starburst colored envelope has a bold multi-color pattern across the face. The pattern stands out in a stack of mail before the envelope is opened. The starburst style uses a peel-and-seal closure with a pressure-sensitive strip, so no moisture is needed. This format suits promotional mailings, direct mail campaigns, seasonal promotions, and any piece where visual impact drives opens.

Browse the complete selection of colored envelopes by size and style.

Number 10 Colored Envelopes

The #10 is the standard business letter envelope. It measures 4-1/8 x 9-1/2 inches with an interior enclosure space of 4 x 9-1/4 inches. It holds a standard 8.5 x 11 sheet folded in thirds and qualifies for First-Class letter postage on contents under 3.5 ounces. Both wove and starburst styles are available in this size.

The #10 colored wove envelope has a solid-color surface and a gum flap closure. Colors include red, beige, and assorted shades for business use. The surface accepts laser and inkjet printing for return addresses and logos. This format suits billing statements, collection notices, gift certificates, and correspondence where color signals a different mail type than standard white envelopes.

The #10 starburst envelope uses the same outer dimensions but has a bold pattern across the face. The peel-and-seal closure needs no moisture, which speeds sealing in small promotional runs. Colors include red, blue, pink, and more. This format suits direct mail, seasonal promotions, and campaigns where the goal is to stand out in a pile of incoming mail.

See the #10 colored wove envelopes and the #10 starburst envelopes for specifications and color options.

Number 9 Colored Envelopes

The #9 envelope measures 3-7/8 x 8-7/8 inches. Its main role is as a reply envelope: a #9 fits inside a standard #10. It can be inserted as a pre-addressed return piece with invoices, statements, donation appeals, or promotional letters.

Color on a reply envelope serves a practical purpose that a white reply envelope does not. When the reply envelope stands out visually from the rest of the letter contents, it is easier for the recipient to notice and act on it. For fundraising and nonprofit development, colored reply envelopes track with higher return rates. They are easier to find when the reader comes back to the piece after setting it aside.

Both wove and starburst styles are available in the #9 format. The wove #9 comes in assorted colors including blue and red. The starburst #9 is available in a range of bright colors including orange, pink, green, blue, lemon, tangerine, cherry, lime, fuchsia, and red. Both use their respective closure types: gum flap for wove and peel-and-seal for starburst.

See the #9 colored wove envelopes and the #9 starburst envelopes for color options and details.

Number 6 3/4 Colored Envelopes

The #6 3/4 envelope measures 3-5/8 x 6-1/2 inches. It is a smaller format than the #9 and is used for short notes, small reply pieces, invoice enclosures, and promotional cards. It also fits inside most #10 envelopes, making it a second reply-envelope option for mailings where a smaller enclosure is preferred.

The wove #6 3/4 is available in vibrant light blue and uses a gum flap closure. The smooth finish works with standard printers for return address and logo printing. Reviewers note using this format in charity campaigns where different envelope colors are assigned to different mailing segments for easy sorting and tracking.

The starburst #6 3/4 comes in pink, green, yellow, red, and blue with a bold pattern on the face and a peel-and-seal closure. This format works well for promotional inserts, holiday cards, and small direct mail pieces where a compact but visually distinctive envelope fits the campaign.

See the #6 3/4 colored wove envelopes and the #6 3/4 starburst envelopes.

6 x 9 Colored Envelopes

The 6 x 9 booklet envelope opens on the long 9-inch edge and holds a standard 8.5 x 11 sheet folded in half, a 5 x 7 card flat, a brochure, or a small catalog. At 6 inches tall, it falls just below the USPS letter-rate height limit of 6-1/8 inches, so it can qualify for First-Class letter postage on light contents under 3.5 ounces.

The 6 x 9 colored envelope is available in the starburst style with a peel-and-seal closure. Colors include yellow, green, and other vibrant options. The starburst pattern on the face makes the 6 x 9 format suited for promotional mailings, event invitations, and campaign pieces that benefit from a larger envelope format and a high-visibility exterior.

For a larger catalog or flat document that cannot be folded, the 9 x 12 format is the alternative (see the next section). For a smaller format that still qualifies for letter rate, the starburst #10 covers that use case.

See the 6 x 9 starburst booklet envelopes for color options and specifications.

9 x 12 Colored Envelopes

The 9 x 12 is a flat-mail format. It holds a standard 8.5 x 11 sheet with about 1/4 inch of clearance on each side and 1/2 inch at the top, so documents arrive without folding. The interior enclosure space is 8.75 x 11.5 inches. USPS classifies the 9 x 12 as a flat rather than a letter, so postage is higher than the letter rate.

The 9 x 12 starburst envelope uses a gummed seal closure rather than peel-and-seal, making it a lower-cost option for this large format. Colors include yellow, pink, lime, blue, and additional options. The starburst pattern makes the piece visible in mail bins before it is opened. This matters for catalog mailings, presentation packets, and flat-mail campaigns where standing out in a stack of standard white flats is the goal.

See the 9 x 12 starburst booklet envelopes for specifications and color options.

How to Use Color Coding in Your Mailings

Color coding assigns different envelope colors to different mailing types, departments, or recipient groups. It is most useful in organizations that process large mailing volumes across multiple purposes and need a quick visual way to sort, track, or prioritize incoming and outgoing pieces.

Common color coding applications in business include:

• Department sorting: Each department uses a different colored envelope for outgoing correspondence, so incoming replies are easy to route without reading the contents
• Campaign tracking: A fundraising or direct mail campaign assigns one color per mailing segment, making it easy to track which segment is generating replies as they come in
• Priority signaling: A colored envelope signals to the recipient that the piece is not routine correspondence and should be opened before standard white mail
• Seasonal campaigns: Using color to match the season or event (holiday, spring campaign, year-end appeal) creates a visual link between the mailing and the occasion
• Reply envelope matching: Matching the reply envelope color to the outer mailing color makes the response piece easier to find and improves return rates

The wove colored envelopes are the practical choice for departmental color coding because the solid color is consistent across the batch, the gum flap is straightforward to seal in volume, and the smooth surface can carry a printed return address or department identifier. The starburst style is better suited when visual distinctiveness is the primary goal rather than systematic color assignment.

Direct Mail and Promotional Uses

In a direct mail context, envelope design affects whether the piece gets opened. Most business mail arrives in a standard white #10 envelope. A piece that arrives in a colored envelope with a bold pattern stands out from that baseline before the recipient makes any decision about its contents.

The starburst envelope series is designed for this role. The pattern is intentionally eye-catching rather than conservative, which makes it appropriate for promotions, limited-time offers, seasonal sales, event announcements, and campaigns where urgency or excitement is part of the message. Because the starburst peel-and-seal closure does not require moisture, it is practical for small-batch runs where sealing by hand is faster than setting up a mailing machine.

For promotional use, the size selection matters as much as the color. A #10 starburst keeps postage at letter rate and holds a standard letter or one-page offer. A 6 x 9 starburst holds a half-fold brochure and may qualify for letter-rate postage.

A 9 x 12 starburst holds a full catalog or product sheet flat, but requires flat-mail postage. Match the size to what you are mailing and your postage budget.

When to Use Colored Reply Envelopes

A reply envelope is most effective when it is easy to find after the recipient has reviewed the mailing. A colored reply envelope is easier to locate in a stack of papers than a white one, which can blend into the letter contents or get set aside with other documents.

Situations where a colored reply envelope improves response rates include:

• Fundraising and nonprofit development appeals: The colored reply piece stands out from the appeal letter and accompanying materials, making it easier for the donor to find and use after deciding to give
• Invoice and billing reply envelopes: A colored #9 or #6 3/4 inside a billing statement envelope makes the payment return piece immediately visible
• Event RSVPs: Colored reply envelopes signal urgency and make the response mechanism stand out from the rest of the invitation package
• Political and advocacy mail: Colored reply pieces are standard in advocacy mail where the goal is a fast, high-volume response from the recipient list

The #9 colored envelope is the most commonly used reply format because it fits inside a standard #10 outer envelope. The #6 3/4 is a smaller alternative for compact mailings. Both are available in wove and starburst styles, though the wove format is typically more appropriate for professional correspondence and billing, while the starburst format fits better in promotional and campaign contexts.

Custom Printing on Colored Envelopes

All colored envelope formats on this site support custom printing. The standard option is a logo and return address printed on the face of the envelope in one or two colors. Custom printing is available on blank stock across the #6 3/4, #9, and #10 wove formats, and on the starburst formats in all sizes.

Custom printing on a colored envelope requires a proof before production. The printing goes on top of the envelope's surface color or pattern, so logo placement and color contrast matter more on a colored envelope than on a standard white envelope. A logo in a dark color stands out on a light wove background. On a starburst pattern, a logo typically works best placed in a solid-color area of the face rather than over the pattern.

Blank stock ships same or next business day. Custom printed orders ship 7 to 10 business days after proof approval. For seasonal campaigns, this lead time should be factored into your mailing schedule.

How to Choose the Right Colored Envelope

The right colored envelope depends on the type of mailing, the size of the document you are sending, and the goal of the piece.

For color selection on wove envelopes, match the color to your brand palette or to the purpose of the mailing. A bold red signals urgency, blue reads as professional, and lighter shades work well for reply envelopes that should be distinctive but not dominate the mailing package.

For size selection, start with what you are mailing. A standard folded letter fits in a #10 format. A flat document needs the 9 x 12. A small enclosure or reply piece uses the #9 or #6 3/4.

Choose the style (wove or starburst) based on whether the goal is professional correspondence or promotional visibility.

Browse the full range of colored envelopes by size and style to find the right format for your next order.

What Is a Double Window Envelope?

A double window envelope has two rectangular openings cut into the face of the envelope and covered with clear poly-film. Each window is positioned to align with a specific address block on the document inside. The upper window on the left side shows your company name and return address as printed on the check, invoice, or statement. The lower window shows the recipient's name and mailing address from the same document.

Because both addresses come from the document itself, you do not need to print separate address labels or hand-write the envelope. The document does all three jobs: it carries the content, it shows who sent it, and it shows who receives it. This is why this format is standard for volume check runs, monthly statement cycles, and accounts receivable invoice mailings.

For a complete selection of formats organized by use case, see the double window envelopes category page.

How the Two Windows Work

The position of each window is fixed to match the address layout of a specific document type. For a business check, the upper window aligns with the company name and return address printed in the upper portion of the check, and the lower window aligns with the payee's name and address printed below. When you fold the check so these address blocks land directly behind the two window openings, both addresses are visible from outside the envelope without any additional printing or labels.

For invoice and statement envelopes, the same logic applies. Your billing software prints the invoice with your return address in the upper portion of the document and the customer's address in the address zone below. Fold the invoice to the correct fold position, insert it, and both windows show the right information. The window placement on these envelopes meets USPS postal automation requirements, which allows the envelopes to be processed by automated letter-sorting equipment at the letter-rate postage class.

The clear poly-film used for the window panels is laser-safe, meaning it does not warp, wrinkle, or distort when the envelope passes through a laser printer or high-speed mailing equipment.

Single Window vs Double Window: What Is the Difference?

A single window envelope has one opening, typically positioned at the lower left of the face. It shows the recipient's address from the document inside. Your return address must be printed separately on the face of the envelope or applied as a printed label. A double window envelope adds a second opening at the upper left, which shows your return address directly from the document inside.

For most check and invoice operations, the double window format is the better choice for blank stock because it removes two steps from the mailing workflow: printing a return address on the envelope and applying a separate label. If you already use pre-printed envelopes with your return address on them, a single window envelope can handle recipient addressing on its own.

Browse the regular business envelopes category for single window and standard formats.

Check Format Double Window Envelopes

Check envelopes use an #8 format that measures 4-1/8 x 9-1/2 inches, the same outer dimensions as a standard #10 business envelope. The difference is window position and document type. The two windows on a check envelope are positioned to align with the address zones on standard business check layouts: the upper window shows your company's name and return address from the top portion of the check, and the lower window shows the payee's address from the address zone below.

The 24 lb white wove stock with a smooth finish is the same weight used in standard #10 business envelopes. The interior security tint is a printed pattern on the inner surface that blocks check contents, including the check amount, account number, routing number, and memo line, from showing through the envelope body when the envelope is held to light. This is the standard security measure for check mailings that contain sensitive financial information.

Three closure styles are available for check-format double window envelopes:

• Gummed flap: Traditional moisture-activated adhesive; seal by moistening the flap and pressing down; lowest cost per envelope
• Peel-and-seal: Pressure-sensitive adhesive strip protected by a release liner; peel the liner off and press the flap down; no moisture needed; adhesive stays protected in stored inventory
• Flip-and-stick: Exposed adhesive tab on the flap with a matching adhesive panel on the envelope body; fold the tab over and press down; no liner to remove; fastest sealing in high-volume runs done immediately after loading

View the check envelopes with flip-and-stick closure and the check envelopes with peel-and-seal closure for specifications and quantity options.

Invoice and Statement Double Window Envelopes

The #10 invoice and statement format also measures 4-1/8 x 9-1/2 inches. It holds a standard 8.5 x 11 sheet folded in thirds, with the address zones aligned to show through the two windows when the sheet is folded correctly. The upper window shows your company name and return address, and the lower window shows the customer's name and billing address.

The window placement on #10 invoice envelopes is built for standard billing template layouts used in QuickBooks, Quicken, Sage, SAP, and FreshBooks. The envelope works without margin adjustments in most standard template configurations. A customer review on the flip-and-stick invoice envelope notes a 500-count pack used for regular monthly billing runs, which is the most common quantity for small and mid-size businesses with recurring invoice cycles.

The interior security tint on invoice envelopes blocks account numbers, statement balances, and other sensitive financial information from showing through the envelope body. For a payroll or financial statement mailing, this is the same protection that check envelopes provide, applied to a full-page document instead of a check.

Four #10 double window options are available for invoices and statements:

• Gum seal: Traditional moisture-activated adhesive flap; manual moistening required
• Peel-and-seal: Adhesive strip with release liner; no moisture needed; good for stored inventory
• Flip-and-stick (self-sealing): No liner to remove; fastest sealing for immediate-use runs
• General #10 format: Available as blank stock for custom printing; supports gummed, peel-and-seal, and self-seal variants

See the #10 invoice envelopes with self-sealing closure and the peel-and-seal invoice envelopes for full specifications.

#9 Double Window Envelopes

The #9 two-window envelope measures 3-7/8 x 8-7/8 inches. It is a reply envelope size: a #9 fits inside a standard #10. For businesses that include a return envelope with invoices or statements, the #9 format can be inserted as a pre-addressed reply piece. It is available with a peel-and-seal closure.

View the #9 two-window envelopes with peel-and-seal closure for details.

Choosing a Closure Type

The right closure type depends on how many you are sealing at once and whether you stock them before use. All three closure types produce a secure seal. The difference is in workflow speed and storage behavior.

For businesses that buy envelopes in large quantities and draw from inventory over several weeks or months, peel-and-seal is the safer choice. The release liner protects the adhesive during storage. Flip-and-stick is faster per piece when you load and seal in the same session, but the exposed adhesive is not designed for long-term storage in open inventory boxes.

Gummed flap envelopes are the standard low-cost option. They work well for manual processing in smaller quantities where moisture activation is not inconvenient. For high-volume mailing machine operations, check whether your equipment is designed for gummed, peel-and-seal, or self-seal stock before ordering.

Software Compatibility

These envelopes are designed to align with the address zones in standard check and invoice templates from major accounting and billing software. The window positions match standard template layouts without requiring custom margin adjustments.

Compatible software for the check format includes QuickBooks, Quicken, and Sage. For the #10 invoice and statement format, compatible software includes QuickBooks, Quicken, Sage, SAP, and FreshBooks.

The alignment works because address zones in standard templates are positioned consistently across software versions. If you use a custom template with non-standard address placement, verify the fold position before ordering in quantity. Print a test page on plain paper, fold it, and hold it against the envelope to confirm the addresses fall in the window zones.

For voucher-style checks printed three per page, the check-format envelope works with the same fold position as standard check layouts. If you use a different check format, confirm the address zone position in your accounting software's print settings before placing a large order.

Security Features

The interior security tint is a printed pattern applied to the inner surface of the envelope. When the sealed envelope is held to a light source, the pattern scatters the light and makes the document inside unreadable from outside. The tint is present on all check-format double window envelopes and on the invoice and statement formats on this site. It is not a physical barrier; it is an optical deterrent that blocks casual inspection through the envelope walls.

The security tint covers the full interior surface, not just the area around the windows. The clear poly-film windows do not carry the tint, by design: the window areas are where the address blocks are intended to be visible. The security tint protects the rest of the document, including check amounts, account numbers, routing numbers, and financial statement details, from showing through the paper walls of the envelope body.

The 24 lb white wove stock used on these envelopes is heavier than the 20 lb paper used in some economy envelope formats, which provides an additional measure of opacity beyond the tint alone.

How to Choose the Right Double Window Envelope

Choosing the right two-window format comes down to three questions: what document you are mailing, which accounting or billing software you use, and what closure type fits your mailing workflow.

If your check or invoice template uses a non-standard address placement, print a test copy on plain paper, fold it, and hold it against the envelope before ordering in quantity. The standard window positions on these envelopes are calibrated for the default template layouts in QuickBooks, Quicken, Sage, SAP, and FreshBooks. Custom templates may require a different fold position or a custom envelope with adjusted window placement.

For departments choosing between check and invoice formats: both share the same outer dimensions of 4-1/8 x 9-1/2 inches, but the window positions are different. A check envelope will not correctly align with a standard invoice template, and a #10 invoice envelope will not correctly align with a standard check template. Match the envelope to the document type you are printing.

Custom printing is available for all formats. Orders include a proof before production. Blank stock ships same or next business day. Custom printed orders ship 7 to 10 business days after proof approval.

Browse the complete double window envelope selection to compare formats, sizes, and closure types side by side.

Closure Types: Peel-and-Seal vs Flip-and-Stick

Before choosing a size, it helps to understand the two closure systems used in self-seal envelopes. Both seal without moisture, but they work differently.

A peel-and-seal envelope has a pressure-sensitive adhesive strip protected by a release liner. You peel the liner off, fold the flap down, and press firmly. The liner protects the adhesive until you are ready to seal, which makes peel-and-seal the right choice for envelopes stored in quantity before mailing.

A flip-and-stick envelope has an exposed adhesive tab on the flap and a matching adhesive panel on the envelope body. You fold the tab over and press down. There is no liner to remove, which speeds up sealing in high-volume runs processed immediately after loading.

For a detailed comparison of both systems including tamper evidence, storage behavior, and mailing machine compatibility, see the complete guide to self-seal envelopes on this site.

Number 10 Self-Seal Envelopes

The #10 is the standard business envelope used for most correspondence, billing statements, payroll notices, and general office mail. At 4-1/8 x 9-1/2 inches with an interior enclosure space of 4 x 9-1/4 inches, it holds a standard sheet of paper folded in thirds.

The self-seal version uses a flip-and-stick closure. No liner to remove means fast sealing when you are processing a batch. The 24 lb bright white wove stock has a smooth finish that accepts laser and inkjet printing for in-house return-address runs. A security tint on the interior blocks document contents from view when held to light, which matters for payroll envelopes, statements with account numbers, and any mailing containing sensitive information.

USPS classifies the #10 as a First-Class letter when contents weigh under 3.5 ounces. For most single-page or two-page mailings, this is the most cost-effective postage class available.

Browse the #10 self-seal security tinted envelope for specifications and quantity options.

Window Self-Seal Envelopes

A window envelope has a clear poly-film cutout on the face that lets the recipient's address printed inside the document show through. Self-seal window envelopes combine address elimination with moisture-free sealing, reducing two manual steps in a billing or statement mailing.

The #10 window self-seal is the most common format for accounts receivable, utility billing, and invoice runs. The window position is set to align with the address block on a standard 8.5 x 11 letter folded in thirds. A security tint on the interior keeps the rest of the document out of view. These envelopes are laser-safe for high-speed printer environments.

Window self-seal envelopes mail at First-Class letter rates when contents are under 3.5 ounces. For departments processing hundreds of pieces per mailing, the time saved on addressing and sealing adds up across the year.

See the #10 window self-seal security tinted envelope for details.

Check Envelopes with Self-Seal Closure

Check envelopes are built to the #8 format, which measures 4-1/8 x 9-1/2 inches, the same outer dimensions as a standard #10. They have two windows positioned on the left side. The upper window shows your return address, and the lower window shows the payee's address. This dual-window layout meets USPS postal automation requirements for letter-rate processing.

The flip-and-stick self-seal closure means no moisture and no liner removal. You load the check, fold, and press the tab down. The security tint on the 24 lb white wove paper blocks the check amount and account details from showing through the envelope walls.

These envelopes are designed to align with standard check templates in QuickBooks, Quicken, and Sage. If you print checks through accounting software and mail them in volume, the dual-window format eliminates separate address labels and reduces handling time per piece.

View the double window check envelopes with flip-and-stick for available quantities.

6 x 9 Self-Seal Envelopes

The 6 x 9 envelope is a catalog-style format, larger than the standard #10 but smaller than the full 9 x 12 flat mailer. It measures 6 inches tall by 9 inches wide, with an interior space of 5.75 x 8.5 inches. That gives it enough room to hold a standard 8.5 x 11 letter folded in half, a 5 x 7 photograph, an invitation, a brochure, or a catalog.

One practical advantage of the 6 x 9 is postage. At 6 inches tall, it falls just below the USPS letter-rate height limit of 6-1/8 inches. When the contents keep the total weight under 3.5 ounces and the thickness under 1/4 inch, a filled 6 x 9 can qualify for First-Class letter postage. This makes it a cost-efficient option for promotional mailings, event invitations, and notices that do not need to arrive flat but benefit from a larger format than the standard #10.

The peel-and-seal closure on the 6 x 9 uses a pressure-sensitive adhesive strip protected by a release liner. This is the open-end style, which loads from the top with the flap on the short edge. The 28 lb white wove stock is heavier than standard business envelope paper, which gives the envelope better durability for flat documents.

For a booklet-style 6 x 9 that loads from the long edge instead, the 6 x 9 white booklet peel-and-seal is available. Browse both the open-end and booklet formats on the self-seal envelope category page.

9 x 12 Self-Seal Envelopes

The 9 x 12 is the standard catalog-size flat mailer for business documents. It holds a standard 8.5 x 11 sheet flat with roughly 1/4 inch of clearance on each side and 1/2 inch at the top. Documents that should not be folded, such as contracts, signed letters, certificates, or multi-page proposals, go in a 9 x 12 rather than a tri-folded #10.

The 9 x 12 white booklet peel-and-seal measures 9 inches wide by 12 inches tall, with an interior of 8.75 x 11.5 inches. The booklet style opens on the long 12-inch edge for easy loading of flat documents, brochures, or photos. The 28 lb wove stock handles the extra weight of thick packets.

USPS classifies a 9 x 12 as a flat rather than a letter, so postage is higher than the letter rate. Weigh the filled envelope before applying postage. For the majority of single-document mailings, First-Class flats postage is straightforward to calculate.

See the 9 x 12 booklet peel-and-seal for specs and quantity pricing.

10 x 13 Self-Seal Envelopes

The 10 x 13 is the go-to size when the 9 x 12 does not give enough clearance. It holds a standard 8.5 x 11 sheet flat with about 3/4 inch of clearance on each side and nearly 1 inch at the top. It also holds legal-size 8.5 x 14 documents flat, with about 1/4 inch at the bottom. The wider interior makes it easier to slide thick packets, bound reports, or stapled multi-page documents in and out without bending the corners.

The 10 x 13 is a common format in law offices, accounting firms, healthcare organizations, and government agencies that process significant volumes of document mailings. The wider clearance also protects brochures and catalogs with full-bleed printing, where a tight-fitting envelope would catch the edge of the printed piece.

USPS classifies the 10 x 13 as a flat. For mailings of thick bound packets, weigh the filled envelope to determine whether the piece qualifies as a flat or tips into the parcel rate based on weight and thickness.

The 10 x 13 white peel-and-seal is available in open-end and booklet styles. See the options on the self-seal envelopes page.

Tyvek Self-Seal Envelopes

Tyvek envelopes are made from DuPont high-density polyethylene fiber rather than paper. The material does not tear, does not absorb moisture, and does not soften in humidity. A Tyvek self-seal envelope arrives in the same condition it left your office, even if it passes through rain or sits in a wet mailbox.

The 10 x 13 Tyvek peel-and-seal measures 10 x 13 inches with an interior space of 9.75 x 12.25 inches. The material is rated at 14 lb, which is lighter than paper envelopes but significantly stronger. It has no grain direction and no structural weak points at corners or edges, so it does not develop the corner tears that paper envelopes sometimes show after postal handling. The Kwik-Tak peel-and-seal closure uses a pressure-sensitive adhesive and a protective liner, the same sealing system as the paper peel-and-seal envelopes.

Common uses for Tyvek self-seal include situations where the document must arrive flat and dry regardless of weather or transit conditions:

• Construction bid packages that travel between offices during an open bid period
• Medical record transfers between facilities requiring intact, legible documents
• Pharmaceutical and laboratory mailings where packaging integrity matters
• Architectural and engineering document sets for client or contractor review
• Any flat document shipped in weather where a paper envelope would soften or tear

The 10 x 15 Tyvek peel-and-seal handles oversized documents and thick presentation packets that do not fit in a 10 x 13. The 6 x 9 Tyvek is available for smaller documents and photos that need the same protection at a smaller format.

View the 10 x 13 Tyvek peel-and-seal envelope for full specifications.

Paper Weight and Material Guide

The paper weight affects how the envelope handles, how much it protects the contents, and how it performs through postal processing equipment.

The 24 lb wove used in standard #10 and check envelopes is the same weight used in most business stationery. It handles well through laser printers and inkjet printers for in-house return-address and logo printing. The 28 lb stock used in the larger flat-mailer sizes provides extra stiffness for documents that should arrive uncreased. Tyvek is a different material category: the 14 lb rating reflects the weight of the polyethylene fiber rather than traditional paper density, and it is considerably tougher than either 24 lb or 28 lb paper.

Custom Printed Self-Seal Envelopes

Most self-seal sizes can be ordered with custom printing. The standard option is a logo and return address printed in one or two colors on the face of the envelope. This removes the need for a separate printed return-address label on each piece and gives your outgoing mail a consistent professional appearance.

Custom printing is available on blank stock across most sizes, including the #10, #9, #6 3/4, 6 x 9, 9 x 12, and 10 x 13 formats. Orders include a proof before production. Production and shipping typically run 7 to 10 business days after proof approval. Blank stock ships same or next business day.

For a custom quote or to discuss a specific format, see the options on the self-seal envelopes page or contact the sales team directly.

How to Choose the Right Size and Style

The right self-seal envelope comes down to three questions: what document are you mailing, does it need to arrive flat, and what postage budget are you working with?

If the document fits in a #10 and can be folded, the #10 self-seal is the most cost-effective choice because it ships at letter-rate postage and is faster to load than a flat-mailer format. If the document cannot be folded or must arrive flat, move to the next size up and budget for flat-mail postage. If the mailing happens in a wet environment or the document must survive potential exposure to moisture, Tyvek is the right material regardless of size.

For departments choosing between peel-and-seal and flip-and-stick, the closure type matters most when envelopes are stored in quantity before use. Peel-and-seal protects the adhesive with a liner, so stored inventory stays usable for longer under normal warehouse conditions. Flip-and-stick has no liner to remove, which saves a step when sealing is done immediately after loading during a mailing run.

Browse the complete selection of self-seal envelopes by size and style to find the right format for your next order.

What Is a Clasp Envelope?

A clasp envelope is a large paper envelope used to hold documents, brochures, photos, and other flat materials that cannot be folded. It uses a metal fastener as its primary closure instead of a gummed or adhesive-backed flap.

The envelope is built in a catalog style, also called open-end. The flap is on the short edge. When the flap opens, the long side is what you slide documents into. This design keeps contents flat and protects them from bending at the corners during handling and mailing.

Most are made from brown kraft paper, typically at a weight of 28 lb. The heavier kraft stock holds its shape when filled with a stack of papers and resists creasing during postal transit. The brown color and kraft construction are standard for this envelope type across business and government use.

The clasp itself is a small piece of ribbed, pliable steel. It passes through a punched eyelet in the flap and bends outward to hold it closed. A reinforced eyelet at the punch point prevents tearing from repeated use. Browse the full selection of clasp envelopes to see available sizes and quantities.

How Does the Metal Clasp Work?

The clasp mechanism has two parts: a metal fastener attached to the back of the envelope and a reinforced eyelet hole in the flap. To close the envelope, you insert the two metal wings of the fastener through the eyelet, then bend them outward flat against the flap. The bent wings hold the flap in place without any adhesive.

To open the envelope, you straighten the wings back upright and pull the flap away from the clasp. The fastener returns to its upright position and is ready to be used again. A well-made clasp on a 28 lb kraft envelope handles repeated cycles without the wings breaking off or the eyelet tearing.

The clasp alone provides enough closure for internal document routing, filing, and short-distance hand delivery. When the envelope needs to go through postal handling, the dual-closure design comes into play: most clasp envelopes also have a moistenable gum flap. You moisten the gum strip and press the flap onto the envelope body, adding a sealed layer on top of the clasp fastening. This dual closure keeps the contents secure through the rigors of machine sorting and truck transport.

Clasp Envelope Sizes

These envelopes are available in five standard sizes. Each one is an open-end catalog envelope with the same 28 lb brown kraft construction. The differences are the outside dimensions and the amount of clearance left around the contents.

The 6 x 9 Clasp Envelope

The 6 x 9 is the smallest standard size. It holds an 8.5 x 11 sheet of paper folded in half, 5 x 7 photographs, small booklets, and multi-page packets such as permission slips, brochures, or folded letters. This size is common for internal distribution at schools, offices, and healthcare facilities where documents need to stay together.

Under USPS rules, a 6 x 9 envelope can qualify for First-Class letter-rate postage when it is under 6 1/8 inches tall, under 11 1/2 inches long, under a quarter inch thick, and under 3.5 oz. When filled with multiple sheets, it may exceed these limits and be reclassified as a flat at a higher postage rate.

Browse the 6 x 9 brown open-end envelopes for specifications and ordering.

The 9 x 12 Clasp Envelope

The 9 x 12 is the most common size for business use. It holds a standard 8.5 x 11 sheet of paper flat, without folding, with roughly a quarter to half inch of clearance on each side. This is the right size for most contracts, invoices, certificates, and business correspondence that cannot be tri-folded into a standard #10 envelope.

This size also holds multi-page reports when they are stapled or bound. Stacks of 20 to 30 unbound sheets fit inside with the clasp closed. Heavier loads may cause the flap to not lie fully flat, in which case adding a strip of tape over the flap provides additional security. See the 9 x 12 brown open-end envelope product page for details.

The 9 1/2 x 12 1/2 Clasp Envelope

The 9 1/2 x 12 1/2 adds about a quarter inch of clearance on each side compared to the 9 x 12. This extra room makes it easier to slide documents in and out without catching the edges. It is a good choice for brochures and catalogs that have a full bleed to the edge of the page, where even a small catch against the interior wall could cause a bend.

The 10 x 13 Clasp Envelope

The 10 x 13 holds legal-size documents (8.5 x 14 inches) without folding, with about a quarter inch of clearance at the bottom. It also holds standard 8.5 x 11 sheets flat, with about 1 inch of clearance on each side and nearly 1 inch at the top. That extra room makes it practical for bound multi-page submissions, thick stacks of 30 to 40 pages, and any document that is difficult to remove from a tighter fit.

Law offices, accounting firms, title companies, and architecture and engineering firms use this size for their standard document mailings and client deliveries. View the 10 x 13 brown open-end envelope for specifications.

The 10 x 15 Clasp Envelope

The 10 x 15 is the largest standard size. It holds oversized documents, thick bound materials, catalogs, and presentation packets that do not fit in a 10 x 13 envelope. This size works for promotional mailings, large-format submissions, and any document or packet too bulky for a standard catalog size.

What Documents Fit in Each Size?

The right size depends on the document you are mailing and whether it can be folded. Folding a contract, certificate, or brochure creases the paper and may make it difficult to use. Choosing a clasp envelope large enough to hold the document flat avoids this problem.

When in doubt, choose the next size up. A document with a bit of extra clearance is easier to remove and less likely to be bent during handling than one forced into a tight fit.

When to Use a Clasp Envelope

Use this type of envelope when the document cannot be folded, when the document needs to arrive flat, or when the envelope will be opened and reclosed more than once. The clasp closure makes it practical for situations where a sealed gummed envelope would need to be torn open each time.

Common situations where this format is the right choice:

• Contracts and legal documents: A signed contract with multiple pages should arrive flat. Folding a multi-page contract creates creases that may cause pages to stick together or pull apart at the fold.
• Certificates and awards: A certificate with a seal, embossing, or printed border should not be creased. A 9 x 12 or 10 x 13 clasp envelope keeps it flat from desk to mailbox to recipient.
• Medical records: Healthcare offices use clasp envelopes to transfer patient records and lab results between facilities. The envelope keeps documents organized and flat during hand-off or mailing.
• Architecture and engineering drawings: Documents printed at letter or legal size for review packets should lie flat in the envelope. A 10 x 13 or 10 x 15 clasp envelope works for most letter-size and legal-size drawing packets.
• Interoffice routing: Internal mail that travels between departments or buildings does not always need a sealed envelope. The clasp closes and opens without any adhesive, so the same envelope is used again for the reply or the next routing.
• Photo mailings: A 6 x 9 clasp envelope holds a 5 x 7 photo without bending. Adding a piece of cardboard inside provides extra protection during postal transit.
• Marketing and promotional packets: A brochure, flyer, or promotional letter sent in a catalog envelope arrives flat and makes a cleaner impression than a folded piece pulled from a standard business envelope.

Clasp vs. Standard Envelope: What Is the Difference?

A standard business envelope, such as a #10, is designed to hold folded documents. It seals with a gummed or peel-and-seal flap and is not meant to be reopened after sealing. A catalog-style envelope with a clasp is designed to hold flat, unfolded documents and can be opened and closed repeatedly.

If the document needs to arrive flat, choose the clasp format. If the document can be tri-folded and the envelope will be sealed once, a standard business envelope is the simpler and less expensive option. For standard business mail, see regular business envelopes.

Can You Mail a Clasp Envelope?

Yes. Clasp envelopes are accepted by USPS. For most sizes, USPS classifies the piece as a flat rather than a letter. Flats are larger pieces that do not qualify for the standard First-Class letter rate and require a higher postage amount, typically USPS First-Class Mail Flats.

The USPS flat rate applies to pieces that exceed any one of the letter limits. For First-Class letters, the piece must be no more than 6 1/8 inches tall, 11 1/2 inches long, and 1/4 inch thick, with contents under 3.5 ounces. A 9 x 12 or larger envelope exceeds the height and width limits for a letter and is therefore classified as a flat.

A 6 x 9 envelope that is under 6 1/8 inches in its short dimension, under 11 1/2 inches in its long dimension, under 1/4 inch thick, and under 3.5 ounces can qualify for letter-rate postage. When the contents bring it above any of those limits, it becomes a flat. Weigh the filled envelope before applying postage to confirm the rate.

The metal fastener does not disqualify an envelope from USPS mail. USPS machines handle these envelopes regularly. Seal the gum flap in addition to using the clasp when mailing, to provide full closure during automated sorting.

How to Seal and Address a Clasp Envelope

Using this type of envelope takes a few more steps than sealing a standard envelope, but the process is straightforward once you do it once.

1. Insert the documents: Slide the contents into the open end of the envelope, short edge first. Make sure pages are aligned and nothing extends past the envelope edge.
2. Fold the flap down: Fold the gum flap over the opening. Do not seal it yet.
3. Thread the clasp: Find the two metal wings of the clasp fastener. They should be pointing upward through the eyelet hole in the flap.
4. Bend the wings outward: Flatten each wing to the sides, pressing them against the flap surface. The flap is now held closed by the clasp.
5. Seal the gum flap (for mailing): Moisten the gum strip on the inside edge of the flap with water or a damp sponge. Press the flap firmly against the envelope body and hold for a few seconds. For mailing, use both the clasp and the sealed flap.
6. Address the envelope: Apply the recipient's address on the front. Use a self-adhesive address label or print directly on the envelope face. Add your return address in the upper left corner.
7. Apply postage: Weigh the filled envelope to determine the correct postage. Use the appropriate USPS First-Class Flats rate for envelopes larger than the letter size limits.

Using Clasp Envelopes for Internal Routing and Storage

One of the main advantages of the clasp closure is that it allows repeated use. In interoffice routing, a single envelope can travel between departments, be opened at each stop, have documents added or removed, and be reclosed without needing a new one each time.

For internal routing, the gum flap is typically not sealed. The clasp alone holds the flap closed during hand delivery within a building or between offices. This keeps the contents secure without committing to a one-time seal.

These envelopes are also used for document storage and filing. An envelope filled with a packet of receipts, a contract with attachments, or a project folder can be labeled on the outside and stored in a file drawer. The metal fastener holds it closed in storage, and the envelope can be opened and closed as documents are added or retrieved over time.

The 28 lb kraft construction makes these envelopes durable enough for repeated handling. The reinforced eyelet at the clasp punch point prevents the hole from tearing through the flap even after many open and close cycles. One envelope used for internal routing can be reused many times before it needs to be replaced.

To find the right size and quantity for your business or office needs, browse the full selection of clasp envelopes available in sizes from 6 x 9 to 10 x 15 inches.