Most envelopes are built for one trip. Clasp envelopes are built for the contents inside them. The metal clasp closure holds the flap shut without glue, which means the envelope can be opened, resealed, and reused. The 28 lb brown kraft construction is heavier than a standard mailing envelope by design, because documents mailed flat in a large format need real protection in transit. At Business Envelopes, we carry brown kraft clasp envelopes in five standard sizes with a dual closure system: metal clasp plus moistenable gum flap. Every size ships free with no minimums across the contiguous 48 states.
What Is a Clasp Envelope?
A clasp envelope is a catalog-style envelope made from kraft paper and sealed with a metal fastener that threads through a reinforced eyelet on the flap. To close it, you bend the metal prongs flat over the eyelet. To reopen it, you straighten the prongs back up. No tearing, no cutting, no damage to the envelope. That reopenable closure is what separates clasp envelopes from standard gummed envelopes and makes them useful beyond a single mailing. Offices use them to circulate internal documents between departments. Law firms use them to organize case files. Schools use them to send home permission slips and retrieve them back.
Our clasp envelopes also include a gummed flap as a second closure layer. For mailing, you fold the flap down and moisten the gum strip in addition to fastening the clasp. That combination gives you a more secure seal than either method alone, which matters when an envelope is traveling through automated postal sorting.
Brown Envelope Sizes: Which One Do You Need?
Getting the size right matters more with flat-mail envelopes than with folded letter mail. A document mailed unfolded needs an envelope that fits cleanly without bending the corners. Here's how each size in our lineup maps to real use cases:
6 x 9 Brown Clasp Envelope
The smallest size we carry. Fits a standard 8.5 x 11 sheet folded in half, a 5 x 7 photo, permission slips, small booklets, or a stack of cards. Popular for school use, interoffice routing, and personal document storage. Compact enough to keep in a desk drawer as a filing tool.
9 x 12 Brown Clasp Envelope
The most widely used clasp envelope size in offices and schools. Fits an 8.5 x 11 sheet flat without any folding, which keeps contracts, reports, certificates, and forms arriving in the same condition they left in. This is the standard for interoffice mail circulation and the go-to for sending anything that can't be creased.
9 1/2 x 12 1/2 Brown Clasp Envelope
A quarter-inch larger on each side than the standard 9 x 12. That extra clearance matters when your document has a printed border that you don't want compressed against the envelope edge, or when you're inserting a 9 x 12 document along with a cover sheet. Also fits manuscripts, brochures, and magazines that run slightly wider than a standard letter sheet.
10 x 13 Brown Clasp Envelope
One step up in both dimensions, built for legal-size documents, architectural drawings at reduced scale, large certificates, and art projects. Accounting firms and legal offices tend to keep these in stock alongside 9 x 12s because not everything fits the smaller size without bending. The extra inch gives you real working room for thicker content stacks too.
10 x 15 Brown Clasp Envelope
The largest size we carry. Fits oversized documents, folded posters, rolled artwork laid flat, large charts, and multi-page bound materials. Used by design studios, architecture firms, and schools for sending home large-format student work. When a 10 x 13 isn't quite enough, this is the next call.
What Are Brown Clasp Envelopes Used For?
The combination of kraft construction, flat format, and reopenable closure makes these envelopes useful in more settings than a standard mailing envelope. Common applications include:
- Mailing contracts, proposals, and legal documents flat without folding
- Interoffice document circulation where the same envelope gets reused across multiple recipients
- School correspondence: report cards, permission slips, assignments, and art projects
- Filing and storage of receipts, photos, invoices, and records that need to stay flat
- Direct mail for catalogs, brochures, and marketing materials that need to arrive unfolded
- Real estate and legal offices sending certificates, deeds, or multi-page packages
The reusability factor is worth emphasizing. A standard gummed envelope is one-use. Once you open it, the flap can't be resealed cleanly. A clasp envelope can be opened and refastened dozens of times without losing function, which makes it a practical tool for document routing and file organization, not just outbound mailing.
Why Businesses Have Trusted Us Since 1997
There are cheaper clasp envelopes on the market. They're usually thinner, the metal clasp is lighter gauge, and the eyelet that the prongs thread through isn't reinforced. That combination means torn eyelets after two or three uses, prongs that won't hold their bend, and kraft paper that creases or punctures in transit. We hear about it regularly from customers who switched back after trying a lower-cost option.
Our brown kraft clasp envelopes are built to 28 lb stock, the same weight commercial print shops specify when they need an envelope to survive real handling. The metal clasp is a ribbed, pliable design that bends cleanly, holds securely, and straightens back without breaking. The reinforced eyelet is punched and finished, not just die-cut. And the dual closure system means that for mailing, you have both the clasp and the gummed flap working together, not just one mechanism asked to do the job of two.
No minimums, no shipping charges on any order across the 48 contiguous states, and bulk pricing that scales with quantity. If you're ordering regularly in volume, request a custom quote here. For other large-format envelope options, browse our full size catalog, or check out our Tyvek envelopes if you need puncture and tear resistance for heavier or more valuable contents.
Frequently Asked Questions About Clasp Envelopes
What sizes do brown clasp envelopes come in?
Five sizes: 6x9, 9x12, 9.5x12.5, 10x13, and 10x15 inches. All 28 lb brown kraft with a metal clasp and gummed flap dual closure.
Can you mail clasp envelopes through USPS?
Yes. Clasp envelopes mail as flats through USPS. Fasten the clasp and moisten the gum flap before mailing. Postage is based on weight and dimensions under USPS flat-rate guidelines.
What is the most common clasp envelope size?
The 9 x 12. It fits an 8.5 x 11 sheet flat without folding and is the standard choice for offices, schools, and business document mailing.
Are clasp envelopes reusable?
Yes. The metal clasp opens and refastens multiple times without damaging the envelope. That makes them practical for interoffice routing, document filing, and storage beyond a single mailing.
What paper weight are your brown clasp envelopes?
Our clasp envelopes are made from 28 lb brown kraft stock, heavier than standard mailing envelopes. That weight handles transit, handling, and multiple open-and-close cycles without tearing.
What fits in a 9 x 12 clasp envelope?
An 8.5 x 11 sheet fits flat with room to spare. Also fits multi-page reports, photos, certificates, and folded brochures. It's the right size for most standard business documents.
Do clasp envelopes come with a gummed flap?
Yes. Our clasp envelopes have both a metal clasp and a moistenable gum flap. For mailing, use both. For internal routing or storage, the clasp alone is sufficient.
What is the difference between a 9 x 12 and a 9 1/2 x 12 1/2 clasp envelope?
The 9 1/2 x 12 1/2 adds a quarter-inch on each side. Choose it when contents nearly fill the 9 x 12 or when inserting multiple sheets at once.