Parts of an Envelope

A simple envelope has a lot going on

Most of us use or handle envelopes every day, but do you know how an envelope is constructed? The envelope you design or choose for your desktop publishing projects is just as important as what goes in it.

The size of the piece, type of mailing, budget, and whether or not you'll be using automated equipment to insert the envelope contents affects the style of envelope you can use. You can also choose specific envelope sizes and styles to enhance a personal or business image, invoke a particular action, or create a certain aura.

When discussing envelope options with clients and printers, basic knowledge of envelope construction can help you cut costs and choose the best envelope for the project.

Face or Front

The front of the envelope, usually seamless, may have windows that allow the inside contents to show through. The face of the envelope is where the address, postage, and usually the return address appears.


The back of the envelope, typically left blank, is where the flaps meet to form and seal the envelope.


The flaps are the parts of an envelope that are folded, overlapped, and sealed to enclose the contents. They are typically rectangular or triangular with rounded, tapered, or pointed corners. The typical envelope consists of two side flaps, a bottom flap, and a top flap. The side flaps are folded in first with the bottom flap folded up. They are sealed where they overlap. The top flap is folded over the side and bottom flaps and sealed after inserting the envelope contents.

  • Top Flap: Also known as the seal flap, it comes in four main styles: commercial, wallet, square, and pointed. There are variations to this basic flap style; some types of business reply on remittance envelopes that include a tear-off section on the flap.
  • Side Flap: The sides of the envelope folded to the inside and sealed along the bottom flap form a pocket. Side flaps may be wide or narrow and rectangular or triangular in shape with straight or rounded corners.
  • Bottom Flap: The bottom flap is folded up and sealed along the edges of the side flaps to form a pocket. It may be squarish or triangular, depending on the style of the envelope, with straight, rounded, or flattened corners.


The style of flaps determines the type of seams, the edges where the envelope flaps meet and overlap.

  • Diagonal Seams: Envelopes with pointed or triangular flaps create diagonal seams across the back of the envelope.
  • Side Seams: Running close to the outer edge of the envelope, square or rectangular flaps form side seams.
  • Center Seam: Found on catalog-style envelopes, large square or rectangular side flaps meet and overlap in the center of the envelope.
  • Seam Overlap: The portion of the flaps that overlap to form the seams of the envelope is the seam overlap.


The creases formed at the sides, top, and bottom between the face and the back when all the flaps are folded to the back of the envelope are the folds.

  • Top Fold: Usually scored during manufacturing, the top flap crease is where the top flap is folded to seal the envelope.
  • Side Fold: The side creases along the sides of the envelope separate the front or face of the envelope from the side flaps folded to the back.
  • Bottom Fold: The crease along the bottom of the envelope separates the front or face of the envelope from the bottom flap.

Envelope Openings and Closures

Envelopes have openings and closures with one side left open and unsealed for inserting material. Non-square envelopes are either open-end or open-side. Open-side is the most common, even though most letter mail envelopes appear to open on top. The opening is determined not by the orientation of the top flap but by the length of the side where the opening appears. In addition to the style or position of the flap, envelope closures may be with or without adhesive. Other open areas, such as windows, are for viewing the contents without opening the envelope.

  • Throat: The throat is the space between the top fold and top of the bottom flap that forms the opening where envelope contents are inserted.
  • Shoulder: The shoulder is a portion of the side flaps along the throat where they meet the top fold.
  • Window: Some envelopes have one or more cut-out areas, usually on the face of the envelope, so that a mailing address, return address, or special message shows through from the inside. Windows may be left open or might have a clear or tinted covering. Window envelopes can be custom-designed or purchased with standard window sizes and positions.
  • Open-Side: On rectangular envelopes, when the top flap—the opening—is on the long side of the envelope, it is an open-side envelope.
  • Open-End: Open-end envelopes have the top flap and opening on the short side of the envelope. Catalog envelopes are typically open-end as are many specialty envelopes such as coin envelopes, policy envelopes, and some interoffice envelopes.

Put these components of an envelope together to form standard and custom envelopes in a variety of sizes.

Although envelopes can be custom-ordered in almost any size, there are numerous standard sizes available for almost any use. Using these standard envelope styles saves time and money.

The size and shape of the flaps and type of seams combine to form six main types of envelopes used for the bulk of non-specialty applications.

A-Style or Announcement Envelopes

Open-side envelopes with square, often deep flaps and side seams, these envelopes—also called A-Style or A-Line—can have deckle edges on the top flap and are often used with matching text and cover papers in white and colors. Typical uses of this style are greeting cards, announcements, informal invitations, and small booklets.

Baronial Envelopes

Used for formal invitations and announcements, greeting cards, and distinctive social stationery, this style is an open-side, almost square envelope with pointed flaps and diagonal seams. Inner/outer envelope sets come with the slightly smaller inner envelope ungummed.

Booklet Envelopes

Open-side envelopes with small square or wallet flaps and side seams, these envelopes are ideal for overall printing and mailing. Booklet envelopes are used not only for booklets but for brochures, catalogs, annual reports, and other multipage mailings. They work well with automatic insertion machines.

Catalog Envelopes

Usually, open-end envelopes with wallet-style flaps and center seams, catalog envelopes are used for mailing magazines, folders, reports, catalogs, and other heavy-weight materials. Policy envelopes, used for insurance policies, wills, mortgages, and other legal papers sometimes come with a full-view window on the face.

Commercial Envelopes

Used for business, direct-mail, personal correspondence, and direct-mail-style envelopes, this style includes the standard #10 envelope. Also called business, standard, or officials, these are open-side envelopes usually with commercial style flaps and diagonal seams although some sizes come with side seams and square or pointed flaps. The Monarch is a variation of the #7 ¾ envelope but with a pointed flap. The window version has single or double windows that allow addresses to show through the face of the envelope. They are normally used for invoices or billing statements, paychecks, and receipts.

Square Envelopes

With their large square flaps and side seams, square envelopes are distinctive, but the nonstandard size and shape can increase postage costs. These are used primarily with announcements, advertising, and specialty greeting cards or other mailings where the sender wants to draw attention to the contents.

Specialized Envelopes

Specialized envelope styles and sizes are based on common commercial, catalog, and booklet styles.

  • Clasp Envelopes: Clasp envelopes are catalog-style—open end, center seam construction—but the metal clasp with a reinforced hole on the top flap allows for multiple openings and closings. They may also have gummed flaps for extra-secure closing.
  • Coin Envelopes: Another catalog-style envelope, coin envelopes are small envelopes used to hold and store coins, stamps, small parts, and other small objects. They are non-mailable due to their small size.
  • Expansion / Accordion Envelopes: Gussets along the sides and sometimes the bottom allow for insertion of bulky contents for storage or mailing. Usually constructed of very heavy paper, they may be open-side or open-end envelopes.
  • Interoffice Envelopes: Used to distribute correspondence within a company, interoffice envelopes may be open-end or open-side, have resealable closures, and are usually drilled with holes throughout so that the recipient can easily see when all the contents are removed.
  • Remittance Envelopes: Used for statements, applications, bank deposits, and other types of material where the recipient will be sending something back to the sender, remittance envelopes typically come in commercial 6 ¼, 6 ½, 6 ¾, and 9 sizes but with side seams and an extra-large flap, almost as large as the envelope body, printed with additional messages, special offers or a coupon. The flap may include a perforation. 
  • Ticket Envelopes: Used for movie, concert, and theater tickets, a standard ticket envelope is a small 4.4375 x 1.3125-inch open-side envelope with diagonal seams.
  • Wallet Flap Envelopes: Wallet envelopes in several commercial sizes such as the #10 and #12 have diagonal seams and a large square flap about half the size of the envelope body and extra seal adhesive for added strength and security. These are for mailing legal documents, bank statements, and other bulky contents.
  • Airmail Envelopes: U.S. Airmail envelopes use lightweight 13 to 16 lb. paper and are preprinted with blue and red airmail markings around the edges. They come in a few standard sizes such as #10 commercial regular and window.
  • First Class Envelopes: U.S. First Class Mail envelopes have a green diamond border. Although not required for first-class mail, the markings help ensure that the material receives first-class handling.
  • Security Envelopes: Security envelopes are printed with a tinted or patterned inside, making it harder to see the contents through the paper. Many standard envelope styles such as the #10, #6 ¾, and remittance envelopes are available with security tinting.
  • Padded or Bubble Envelopes: Padded envelopes contain a cushioned lining, such as bubble-wrap material. They help protect small, fragile items from crushing.


Standard size and custom envelopes can have a variety of types of closures. Some may use non-adhesive seals.

  • Seal Adhesive: The strip of adhesive along the edge of the open-top flap used to seal the envelope. Some adhesive requires moistening (such as with water or by licking the edge) and other types require two gum surfaces that press together and seal without moisture. A peel-and-stick adhesive has a strip of waxy paper covering the adhesive until the envelope is ready for sealing.
  • Back Gum: This is a stronger adhesive used to seal the side and bottom flaps of the envelope during manufacturing.
  • Clasp: Some booklet and catalog envelopes have metal or plastic fasteners with or without re-moistenable gum that allows the envelope to be opened and closed repeatedly.
  • String-and-Button: For repeated openings and closings, some envelopes have a metal or paper button with a string that wraps around the button to hold the top flap closed. Expanding envelopes may have elastic strings that stretch around the entire envelope to accommodate the varying size of the contents and hold the envelope closed.
  • Tamper-Evident Seal: Envelopes bearing confidential or sensitive contents can have a special seal that indicates if it has been broken. A window on the flap reveals the word "Opened" if the flap has been opened and reclosed, or the top flap may contain a perforated strip that can only be peeled off once to reveal the envelope contents.

Paper Weight

Standard size and custom envelopes can be printed with many different paperweights.

Standard envelope styles and sizes use specific paper weights, although a designer can request custom paper choices. U.S. Air Mail envelopes use a lighter 13 to 16 lb. paper to keep the cost of overseas mailings lower. Some types of clasp or storage envelopes that are handled a lot, such as in offices, may use heavier 32 lb. to 40 lb. paper. A 20 lb. to 28 lb. paper is typical for most commercial, baronial, and A-style envelopes.

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