A windowed envelope is a conventional

envelope An envelope is a common packaging item, usually made of thin, flat material. It is designed to contain a flat object, such as a letter or card. Traditional envelopes are made from sheets of paper cut to one of three shapes: a rhombus, a shor ...

with a plastic (typically film or BOPS Bi-oriented polystyrene films) window to allow the recipient's address to be printed on the paper contained within.

History

Americus F. Callahan of Chicago, Illinois, in the United States, received the first

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...

for a windowed

on 10 June 1902. Originally called the "outlook envelop", the patent initially anticipated using thin

rice paper "Rice paper" has many varieties such as rice paper made from tree bark to make drawing and writing paper or from rice flour and tapioca flour and then mixed with salt and water to produce a thin rice cake and dried to become harder and paper-like ...

as the transparent material forming the window, though this material has since been replaced by clear plastics. The design has otherwise remained nearly unchanged. The design and patent letter were completed on 15 November 1901, with the patent filing occurring on 9 December 1901. The United States patent number for Callahan's design is 701,839. Callahan specifically recommended the use of

Manila paper Manila paper is a relatively inexpensive type of paper, generally made through a less-refined process than other types of paper, and is typically made from semi-bleached wood fibers. It is just as strong as kraft paper but has better printing qu ...

, which is considerably cheaper than thicker writing paper and also provides an opaque background for secure covering of the letter within. Callahan also recommends the use of black paper, which would likewise provide an opaque background whilst simultaneously increasing the contrast with the white address blocks.

Advantages and disadvantages

The window permits text on the letter itself to be used simultaneously as the address of the recipient and the return-address of the sender, reducing the need to print the addresses onto the envelope itself, which at the time of Callahan's invention was done with the aid of a

typewriter A typewriter is a mechanical or electromechanical machine for typing characters. Typically, a typewriter has an array of keys, and each one causes a different single character to be produced on paper by striking an inked ribbon selectivel ...

. This arguably amounts to a savings in materials, particularly through the reduction in

ink Ink is a gel, sol, or solution that contains at least one colorant, such as a dye or pigment, and is used to color a surface to produce an image, text, or design. Ink is used for drawing or writing with a pen, brush, reed pen, or quill. Thicker ...

usage; but on the other hand the window has to be cut out and sometimes replaced by an additional material called a patch (originally

glassine Glassine is a smooth and glossy paper that is air, water, and grease resistant. It is usually available in densities between . It is translucent unless dyes are added to color it or make it opaque. It is manufactured by supercalendering: after ...

but now plastic). This makes the envelope more expensive. There is also the argument that the paper of the envelope can be substituted with lesser-quality paper as the envelope no longer must be written upon; this perhaps was more relevant at the time of Callahan's invention but is a somewhat specious claim today. Over time the quality of paper generally has improved. Satisfactorily-strong envelopes for business and general-purpose domestic correspondence can be, and are, in fact made out of paper of various qualities. In Britain by the 1940s, during World War 2, envelopes were made out of newspaper because of the paper shortage. Additional savings can be achieved by removing the time spent inscribing additional addresses upon the envelope. At the time, large business offices—particularly within the

telegram Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...

industry—employed corps of envelope addressers who wrote the addresses upon envelopes. In addition to the labor costs, this method was prone to mismatches, where the address on the letter header within would not be the same as the address upon the envelope. Owing to the benefits in both time, cost, and quality, the windowed envelope design has become nearly ubiquitous among modern commercial mailings. Regarding recycling after use: plastic windows are not ''normally'' a problem for paper mills as the window can usually be easily screened out during the manufacturing process.Recycling envelopes
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References

{{Paper Envelopes Postal systems American inventions