Security Envelopes for Business: Types, Sizes, and When to Use Them

Last updated: November 3, 2026

A security envelope looks like a standard business envelope from the outside. The difference is on the inside. A printed pattern on the interior lining blocks the contents from showing through the paper when the envelope is held up to light. For businesses mailing checks, financial statements, salary information, or any document with sensitive details, this simple feature adds a meaningful layer of privacy.

This guide covers how these envelopes work, which types are available, which sizes to choose, and how to match the right closure to your mailing volume.

Quick Summary

This format uses an interior tint pattern printed on the inside of the paper to block the contents from being visible through the envelope wall. The tint is not a coating over the outside. It is printed directly on the interior surface so it cannot be scratched off.

The most common sizes for business use are the #10, #9, and #6 3/4. Closure options include gummed flap, peel-and-seal, and self-seal flip-and-stick.

TL;DR

• The security tint is printed on the inside of the envelope paper. It prevents the contents from showing through when held to light.
• Three main types: security tinted regular envelopes, security tinted window envelopes, and double window security check envelopes.
• Most common sizes are #10 (4 1/8 x 9 1/2 in), #9 (3 7/8 x 8 7/8 in), and #6 3/4 (3 5/8 x 6 1/2 in).
• Closure options are gummed flap, peel-and-seal, and self-seal (flip-and-stick). Peel-and-seal is the most consistent for moderate to high volume.
• These envelopes are compatible with laser and inkjet printers. They accept standard address labels and rubber stamp impressions.
• Contents under 3.5 oz qualify for the USPS First-Class letter rate, the same as standard business envelopes.

What Is a Security Envelope?

A security envelope is a business envelope with an interior pattern that prevents the contents from being seen through the paper. The envelope looks plain white on the outside. Standard business mail does not reveal its contents, but thin paper stock and bright light sources can sometimes make the printing inside faintly visible. The interior tint eliminates that risk.

These envelopes are most commonly used for checks, payroll documents, financial statements, account numbers, and salary information. Any mail where the contents should not be visible to someone handling the piece before it reaches the recipient is a candidate for this format.

This is a standard product in business mail, not a specialty or custom item. It is available in the same sizes and closure types as regular business envelopes and mails at standard USPS First-Class rates.

How Does the Security Tint Work?

The security tint is a pattern printed on the interior surface of the envelope paper. It is not applied to the outside of the envelope and it is not a coating added after the envelope is made. The pattern is part of the envelope's construction.

When light passes through the paper from the outside, the interior tint pattern breaks up the text of the enclosed document. The eye sees the tint pattern instead of the document's content. A check's amount, a salary figure, or an account number becomes unreadable through the envelope wall even under direct light.

This design has two practical advantages. First, the tint is permanent. It cannot be scraped, rubbed, or washed off because it is on the inside of the paper, not the outside surface.

Second, it does not interfere with how the envelope is handled. The outside of the envelope prints, labels, and stamps the same as any standard white business envelope.

The tint pattern itself is typically a geometric or repeating cross-hatch design printed in blue or another contrasting color. The design is dense enough to block show-through without adding meaningful weight to the envelope.

Types of Security Envelopes

Three main formats are available. The right choice depends on whether you need a window, whether you need two address windows, and the type of document being mailed.

• Security tinted regular: No window. Address printed or labeled on the outside. Best for checks, confidential letters, and financial statements.
• Security tinted window: Single clear window for the recipient address. Best for invoices and billing statements where the address is printed on the document.
• Double window security check: Two clear windows for both the payee and return addresses. Used specifically for printed checks in payroll and accounts payable operations.

Security Tinted Regular Envelopes

Security tinted regular envelopes have no window. The outside is a plain white face. You print, handwrite, or apply a label for the recipient's address. These are the most straightforward format and the most commonly used for checks, statements, and confidential correspondence.

They come in sizes #6 3/4, #9, and #10. The #10 size is the standard business envelope size used for most correspondence. The #9 is a common return envelope size. The #6 3/4 suits smaller folded documents and remittance items.

Closures include gummed flap, peel-and-seal, and self-seal flip-and-stick. Browse security tinted regular envelopes to see all available size and closure combinations.

Security Tinted Window Envelopes

Security tinted window envelopes have a clear film window on the lower left of the face. The recipient's address on the enclosed document shows through the window. This eliminates the need to print, type, or affix a separate address label on the envelope.

The interior tint is applied to the paper areas around the window. The window itself is a clear film with no tint. The security protection applies to the paper body of the envelope, not the window area.

These are commonly used for invoices, billing statements, and accounts receivable mail where the document address must align with the window. They require the document to be formatted and folded so the recipient address lands in the window position. See the window envelopes section for available styles.

A laser-safe version is also available in the #10 size. Laser-safe means the envelope and window film can pass through a laser printer without warping or jamming. This suits operations that print the envelope directly rather than printing a separate label.

Double Window Security Check Envelopes

Double window security check envelopes have two clear film windows: one for the payee address and one for the return address. Both addresses are printed on the check itself and show through the windows, so no addressing of the envelope is needed at any point in the process.

These are designed specifically for check mailing. The check slides into the envelope and both address windows align automatically if the check is formatted for double window envelopes. This is the standard format for payroll check runs, accounts payable batches, and vendor payment mailings.

The interior tint blocks the check amount, bank routing number, and account number from showing through the paper. Only the address windows are clear. The check envelopes section includes double window security options in gummed, peel-and-seal, and flip-and-stick closures.

Security Envelope Sizes

These envelopes are available in the same standard sizes as regular business envelopes. The most common sizes cover most business mail needs.

The #10 Envelope

The #10 is the standard size for business mail. It measures 4 1/8 x 9 1/2 inches with an interior enclosure space of 4 x 9 1/4 inches. A standard 8.5 x 11 letter fits inside when folded into thirds. The #10 is the right size for most checks, invoices, statements, and business correspondence.

Security tinted #10 envelopes come in plain (no window), single window, and laser-safe single window versions. The #10 security tinted peel-and-seal envelope is a practical starting point for most business mailing operations.

The #9 Envelope

The #9 measures 3 7/8 x 8 7/8 inches. It fits inside a #10 as a reply envelope. A standard 8.5 x 11 letter fits when folded into thirds or quarters depending on the fold method. This size is common for payroll checks, return remittance envelopes enclosed with statements, and reply envelopes sent alongside an invoice.

The #6 3/4 Envelope

The #6 3/4 measures 3 5/8 x 6 1/2 inches. It is smaller than the #9 and suited for compact remittance items, smaller checks, and folded documents that do not need a full #9 or #10. It is a common choice for retail remittance envelopes and smaller correspondence that does not require a full-size business envelope.

Closure Options for Security Envelopes

Three closure types are available. Each has practical advantages depending on mailing volume and the process used to seal and send mail.

Gummed Flap (Moistenable Glue)

A gummed flap has a strip of dry adhesive on the underside of the flap. Moistening the strip with water, a sponge, or a wet sealing tool activates the adhesive. The flap then seals to the envelope body.

This is the traditional closure for business envelopes. It suits low-to-moderate volume operations where moisture application is straightforward. It is also the most common closure for machine sealing in high-volume mail operations, since folder-inserter machines have built-in moistening elements designed for gummed envelopes.

Peel-and-Seal (Pressure Sensitive)

A peel-and-seal closure has a strip of pressure-sensitive adhesive covered by a release liner. To seal, peel the liner away from the adhesive strip and press the flap firmly onto the envelope body. No moisture is needed.

This is the preferred closure for offices without a sealing machine, for employees sealing envelopes by hand, and for situations where saliva or a wet sponge is impractical. The adhesive bonds on contact and holds through postal handling. It is consistent and fast for hand-sealing batches of any size.

Self-Seal / Flip-and-Stick

A self-seal or flip-and-stick closure has adhesive on both the flap and the corresponding panel on the envelope body. The two adhesive surfaces bond to each other when pressed together. No moisture is needed and no liner needs to be peeled away.

This is a fast, clean closure for high-frequency hand sealing. It is common in customer service and billing operations where envelopes are sealed one at a time throughout the day rather than in a single batch. For self-seal options, see the self-seal envelopes section.

When Should You Use a Security Envelope?

Use a tinted envelope whenever the mailed document contains information that should not be visible from the outside. Common use cases include:

• Payroll checks: Check amount, employee name, and bank details should not be readable through the envelope. Security tinted check envelopes protect this information through the mail stream.
• Accounts payable checks: Vendor payment amounts and bank routing numbers are sensitive. Double window security check envelopes handle these mailings without requiring separate addressing.
• Financial statements: Account balances, transaction histories, and account numbers mailed to customers warrant a tinted envelope.
• Salary information: Any letter containing salary figures, compensation details, or employment offer amounts benefits from a security tinted envelope.
• Medical correspondence: Patient information, billing statements from healthcare providers, and insurance correspondence often contain personal health data that should be protected in transit.
• Legal and compliance documents: Contracts, notices, or documents with case or file numbers that should not be visible to postal handlers.
• Customer account notices: Credit limit changes, rate adjustments, or account status letters that contain account numbers or financial details.

Standard envelopes without security tint are appropriate for most general business correspondence where the contents are not sensitive. If you are unsure, ask whether you would be comfortable with a postal worker, courier, or office mail room employee being able to see through the envelope. If not, choose a tinted format.

Security Envelopes vs. Standard Envelopes: What Is the Difference?

The primary difference is the interior tint. A standard white business envelope has no interior lining beyond the paper itself. Under direct light, thin paper can allow printed text to show through faintly. The interior tint pattern eliminates that risk.

In practice, these envelopes look identical to standard envelopes from the outside. Recipients see no difference. The protection is entirely internal.

How to Choose the Right Security Envelope

Choosing the right envelope for this use comes down to three decisions: size, window type, and closure. Making these decisions in order simplifies the selection.

Match the Size to the Document

Start with what you are mailing. A standard letter or invoice folded in thirds fits a #10. A reply envelope or payroll check fits a #9.

A small remittance or folded compact document fits a #6 3/4. If you are mailing checks formatted for double window envelopes, the #9 double window size is the standard fit.

Do not choose a size smaller than the document requires. A document that is forced into an undersized envelope will crease at the wrong points and may be difficult to remove cleanly at the receiving end.

Decide Between Window and No-Window

If you print the recipient's address directly on the envelope or apply a label, a plain (no-window) tinted envelope is the right choice. If the recipient's address is printed on the document and you want it to show through without re-typing or labeling, use a window version.

Double window check envelopes are appropriate only when the document is a check formatted for that envelope style. Both windows must align with the addresses on the check. Confirm the check format before ordering the envelope.

Match the Closure to Your Volume and Process

For low to moderate volume hand sealing, peel-and-seal is fast and consistent. For high-volume machine sealing, gummed flap is the standard choice because folder-inserter machines are designed for it. For frequent single-envelope sealing throughout the workday, self-seal flip-and-stick is the most practical.

Printing and Labeling Security Envelopes

Security tinted envelopes accept the same printing methods as standard business envelopes. The tint is on the inside. The outside face is plain white wove and accepts print normally.

• Inkjet printing: Standard inkjet printers handle these envelopes without adjustment. Feed one at a time if your printer has a manual envelope slot.
• Laser printing: Security tinted envelopes in standard paper stock (24 lb) are compatible with most laser printers. Laser-safe versions are also available for operations that need guaranteed compatibility with high-heat laser processes.
• Label application: Self-adhesive address labels stick cleanly to the smooth white wove exterior. The surface is not coated, so standard labels adhere well without lifting at the edges.
• Rubber stamps: Return address stamps and business name stamps work the same as on standard envelopes. The ink absorbs into the wove surface cleanly.

Custom printing on the exterior (return address, logo, tagline) is available for orders that meet quantity requirements. The interior tint is not affected by exterior custom printing.

Postage and Mailing Rates

These envelopes mail at the same USPS rates as standard business envelopes. Contents under 3.5 oz in a #10, #9, or #6 3/4 tinted envelope qualify for the USPS First-Class letter rate. There is no additional postage or surcharge for using the security tinted format.

The interior tint adds minimal weight. A standard #10 security tinted envelope with a single tri-folded letter inside will not exceed the 1 oz threshold for the standard First-Class stamp rate in most cases.

Double window check envelopes used for standard payroll checks also qualify for First-Class letter rates when the contents stay under 3.5 oz. Multi-check packets or bulky enclosures may exceed the letter weight limit and require package or flat rates.

To find the right size and quantity for your mailing needs, browse the full selection of security tinted envelopes available in #6 3/4, #9, and #10 sizes with your choice of closure type.