Envelope Manufacturing & Materials

A badly specified envelope causes trouble late in a job: it cracks along a fold, jams the inserter, or shows the address in the wrong place. Envelope manufacturing turns paper into finished envelopes in a few repeatable steps (cutting a blank, adding any window, folding and gluing the seams, and applying seal gum to the flap), and the paper, window and adhesive chosen beforehand decide how the envelope will run and mail.

This section explains those steps and materials for people who buy envelopes, plan mailings or work in envelope converting. It does not list products for sale or give postage prices; postal rules are quoted from current USPS text with the applicable section reference.

Before approving stock for a mailing, use the envelope sizes guide to compare finished dimensions with the converter’s maximum enclosure and check the filled piece against USPS limits. For confidential contents, the security envelope features guide separates interior tint from fiber-tear and closure evidence so the sample approval checks the protection the job actually needs.

How an envelope is made

Envelope machines start either from a paper reel (the web) or from a stack of pre-cut blanks; a blank is paper die-cut to the flat shape of an envelope before folding. The Envelope Manufacturers Association (EMA) guide notes that diagonal-seam envelopes are usually cut as blanks on a die press and then folded and gummed, while side-seam envelopes are more often cut from a web by a die-cutting unit on the folding machine itself, with exceptions both ways. One machine family, the W+D 628, is offered in reel-fed, blank-fed and combined versions; its published layout gives an example of the stations:

1. Feed. A reel is unwound and aligned, or blanks are fed from a stack.
2. Print (optional). Rolls or blanks can be printed beforehand by offset or digital presses, or printed inline by flexo units on the machine, on the outside and on the inside. The anilox band that separates those two ink paths is in the flexo versus offset litho note.
3. Cut and score. On a reel-fed line, the envelope shape is form-cut from the web and separated. On a blank-fed line, rectangular blanks can be form-cut on the machine, while blanks already die-cut to shape skip this cut. Score lines then prepare each fold.
4. Window (optional). The window opening is cut and a film patch is glued to the inside.
5. Fold and seam. Side flaps are folded and gummed, then the bottom flap is folded, forming the pocket.
6. Seal flap. Gum is applied to the seal flap, dried (this layout uses a heated drying section) and the flap is folded. The same machine family can apply dextrin, latex or hot-melt pressure-sensitive adhesive.
7. Deliver. Finished envelopes are counted and stacked for packing.

Stations and their order vary by machine and options; envelopes without windows skip step 4.

For what happens to the paper at each step, which glue does which job and what to inspect along the way, see how envelopes are made, step by step.

Takeaway: When comparing suppliers or machines, ask which route (web or blank) and which optional stations a given envelope needs.

Key topics in envelope making

Paper

Common envelope papers include wove, a short-fiber paper with a smooth surface that prints well, and kraft, a paper with longer, stronger fibers that prints less well. Weight is quoted as basis weight. For bond, wove and kraft, that is the weight of 500 sheets of 17 × 22 in paper, so 24 lb works out to about 90 gsm. The EMA guide stresses grain direction: folding against the grain can crack and curl the paper, so it recommends running the grain the long way on open-end envelopes, the short way on open-side booklets, and diagonally on diagonal-seam envelopes. Treated and synthetic papers are less porous and may need special adhesives; for flash-spun high-density polyethylene mailers compared against heavy cellulose catalog stock, see Tyvek vs. kraft paper envelope durability, moisture resistance, and ink adhesion.

Windows

The window films the EMA guide names include cellophane, glassine, polystyrene, polypropylene, polyester, acetate, colored films and PLA. Whatever the film, it must be clear, tight and wrinkle-free so that it does not hide the address, and envelopes printed on high-heat printers after converting need heat-tolerant film.

Adhesives

An envelope carries up to three adhesives: back-seam adhesive holds it together, window-patch adhesive holds the film, and seal-flap adhesive closes it later. Moisture-activated seal gums are made from dextrin, resin or a blend of the two, applied as a thin film and dried. Latex self-seal uses two patterns that stick only to each other, and pressure-sensitive seals sit under a release strip. The same choice between a pre-applied adhesive and glue applied at the point of use appears in labeling; see pressure-sensitive vs wet-glue labels.

Before choosing a seal-flap adhesive, compare self-seal vs gummed envelopes: the guide separates two-band latex closures from liner-backed peel-and-seal and provides a record for checking storage and machine requirements.

Construction and flaps

Most envelopes use closed-seam construction, with at least three folds and gum only on the overlapping edges, which is the construction inserter specifications emphasize. The EMA guide calls flaps the least standardized part of an envelope, shaped by the machine, the printer’s needs, the bulk of the mailing and the gum. How the opening and seams combine into named styles (business, catalog, booklet and others) is covered in Types of Mailing Envelopes.

For donation appeals, statement returns, and dual-purpose reply mailings, compare full-face wallet flaps, perforated drop-seal stubs, bangtail coupons, and return insert clearances in the remittance envelopes guide.

For flat mailings, catalogs, and bound reports, compare open-side versus open-end flap geometry, inside side seams versus center seams, and expansion gussets in the booklet vs. catalog envelopes guide.

Inspection

The EMA guide gives about ±1/16 in as normal machine variation, because machines heat up and parts wear. That is a rule of thumb, not a contract tolerance, so state a tolerance when exact dimensions matter. On receipt, check the finished size, the window position against the real insert, the gum lines (including excess gum around windows) and the print.

Common mistake: Approving a window envelope from a drawing alone. The window position has to be checked with the actual insert, because small shifts in the form or the window can hide part of the address.

Takeaway: Specify paper grade and grain, window film, closure and tolerance together; they affect one another on the machine.

Common specification questions

For small parts and seed packets, use the coin envelope size chart and filled-part checks to compare numbered pockets, inspect seams and choose an outer mailing package.

Questions buyers ask when ordering envelopes, and what each one decides:

• “Blank or printed and if so how many colors on front and back?” Decide whether the envelopes arrive plain or preprinted, and list the colors for each side.
• “Windows or no window?” A window saves addressing the envelope separately but ties the envelope to the form layout.
• “Type of paper / Standard 24# White Wove?” Give the grade and the basis weight, for example 24 lb white wove (about 90 gsm).
• “Type of gum?” Moisture-activated gum is the most common, and the EMA guide attributes that to its suitability for automatic inserting machines. Latex self-seal and peel-and-seal close by pressure rather than moisture, and Tension states that its peel-and-seal is not compatible with automatic inserters.
• “Can you make your own envelope for USPS?” USPS rules apply to the finished, filled piece, whoever made the envelope. A retail letter, for example, must be rectangular and between 5 × 3-1/2 in and 11-1/2 × 6-1/8 in, and no more than 1/4 in thick (DMM 101). The envelope types guide shows the letter and flat limits.

For how address hygiene, printing, mechanical inserting and postal traying fit together after envelope converting, see the mailing, inserting and fulfillment overview.

Takeaway: An envelope order is complete when it names style and size, paper, window, print colors, closure and how the envelopes will be filled.

Envelope terms

Term	Meaning
Blank	Die-cut paper in the flat shape of an envelope, before folding
Score	A prepared line that helps the paper fold cleanly
Throat	The opening at the top of the envelope, where the contents go in
Seal flap	The flap that folds over to close the envelope
Open end / open side	Opening on the short edge / on the long edge
Side, diagonal and center seam	Where the permanent back seams run: near the sides, diagonally across the back (corner to corner, in the EMA glossary), or down the middle
Window patch	The transparent film covering a window opening
Glassine	A transparent, highly hydrated paper used for windows
Remoistenable gum	Seal-flap gum reactivated with moisture
Latex self-seal	Two adhesive patterns that stick only to each other when pressed
Basis weight	Weight of 500 sheets at the grade’s basic size; 17 × 22 in for bond, wove and kraft
Converting	Turning reels or blanks into finished envelopes; separate from inserting, which fills them

Takeaway: Use these terms in a specification so the converter and the mailing house read it the same way.

When this does not apply

• Protective mailers. The route above describes paper envelopes. Padded, bubble and poly mailers use different materials and constructions; see paper mailers vs poly mailers.
• Papermaking. Making the paper itself is a separate, earlier process and is not covered here.
• Postal rules outside the United States. Size limits quoted on these pages are USPS domestic rules.

The history of Mail-Well, Inc. is covered separately in the Historical Archive.

Takeaway: For these cases, use a source written for that case.

Sources and method

The process route follows one published machine layout as a representative example. The EMA guide’s postal figures were not used; current postal limits are quoted from DMM 101. See the editorial policy for how sources are chosen and checked.

• The EMA Guide to Envelopes and Mailing, Envelope Manufacturers Association (PDF; file metadata dated 2015; its postal figures are not used here).
• W+D 628 envelope machine brochure, Winkler+Dünnebier, hosted by BW Converting (used for the station layout; not an endorsement of the machine).
• Glossary of Envelope Terms, Envelope Basics: Closures and Window Technology at Tension, Tension.
• DMM 101 Physical Standards and DMM 201 Physical Standards, USPS Postal Explorer.

Takeaway: Recheck the dated postal limits before relying on them for a mailing.