Custom Window Envelopes are used frequently in direct mail and in smaller specialized applications. In envelope parlance, a custom window is also referred to as a special window: same thing; different terminology.
A standard window measures 1-1/8” x 4 ½” and is placed 7/8” in from the left edge and ½” up from the bottom edge. (See diagram) Since the use of bar-coding for outgoing mail has become more common, there are a couple of different envelope window sizes that have become near-standards. They are close to the standard size and placement but generally a little bigger and/or placed a little higher up from the bottom in order to incorporate the bar code either as part of the address showing through the window or ink-jetted at the bottom of the envelope below the window. These can vary from company to company so it’s always better to check before designing your mail piece.
The standard window was originally designed to display the outgoing address when it’s typed in the customary spot on the upper left-hand corner of a standard 8 ½ x 11 letter sheet and tri-folded to fit in a standard #10 envelope. That is still the case and the standard #10 window envelope is by far the most widely used window envelope. If your mailing can be designed to use the standard window, it’s going to be less expensive especially in smaller quantities of 100,000 or less. On any mailing of over 100,000 there will be less of a difference in price for using a custom window and the price difference nearly disappears on very large quantities of 1 million or more. Envelope manufacturing is the same as any other kind of custom manufacturing: the larger the quantity, the lower the unit cost.
Most window envelopes have a patch over the window which is glued to the inside of the envelope. This protects the contents and makes them more secure. Unpatched window envelopes are more commonly used for reply envelopes where the end –user is handling the piece individually; mostly on large mailings for utilities and insurance companies. Putting a window envelope with no patch covering the window through a mailing machine could cause problems which is why this is rarely done.
In order to properly glue a patch to the inside of an envelope, you must have a minimum of 3/8” space from the edge of the envelope to the edge of the window cut-out. Most envelope converters will not make a window with less space than that.
Window patch material can vary. The most common is the regular poly material which is a clear plastic. In the past, glassine was used as a recyclable alternative to poly but had drawbacks due to the fact that it was cloudy and not favored by the post office. More recently, there have been numerous vegetable based window materials that are clear but also recyclable. These tend to be more expensive as is typically the case with any recycled material including paper.
Custom windows can vary widely in both size and shape. A commonly used item is the full-view window. This is a large window used generally on a #10, 6 x 9 or 9 x 12 size envelope that covers most of the face of the envelope. It allows for whatever piece is inserted to show through almost completely which can entice the recipient to open the envelope. Other popular custom windows are the pistol shape and basic geometric shapes like circles and squares. The former is generally used to show an address while the latter are used to expose certain spots of the mail piece to create curiosity on the contents. The creative use of custom windows is a great way to get the recipient to open the envelope which, after all, is the whole point.