A windowed envelope is a conventional envelope

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....

 with a plastic window to allow the recipient's address to be printed on the paper contained within.

History

Americus F. Callahan of Chicago

Chicago

Chicago is the largest city in the US state of Illinois. With nearly 2.7 million residents, it is the most populous city in the Midwestern United States and the third most populous in the US, after New York City and Los Angeles...

, Illinois

Illinois

Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...

, in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, received the first patent

Design patent

In the United States, a design patent is a patent granted on the ornamental design of a functional item. Design patents are a type of industrial design right. Ornamental designs of jewelry, furniture, beverage containers and computer icons are examples of objects that are covered by design...

 for a windowed envelope

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....

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

Rice paper

Rice paper usually refers to paper made from parts of the rice plant, like rice straw or rice flour. The term is also used for paper made from or containing other plants, such as hemp, bamboo or mulberry...

 as the transparent material forming the window, though this material has since been replaced by clear plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

s. 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

United States Patent and Trademark Office

The United States Patent and Trademark Office is an agency in the United States Department of Commerce that issues patents to inventors and businesses for their inventions, and trademark registration for product and intellectual property identification.The USPTO is based in Alexandria, Virginia,...

 for Callahan's design is 701,839.

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

Typewriter

A typewriter is a mechanical or electromechanical device with keys that, when pressed, cause characters to be printed on a medium, usually paper. Typically one character is printed per keypress, and the machine prints the characters by making ink impressions of type elements similar to the pieces...

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

Ink

Ink is a liquid or paste that contains pigments and/or dyes and is used to color a surface to produce an image, text, or design. Ink is used for drawing and/or writing with a pen, brush, or quill...

 usage; but on the other hand the window (or "patch" as it is known in the envelope manufacturing industry)has to be cut out and replaced by an additional material(nowadays glassine

Glassine

Glassine is a very thin and smooth paper that is air and water resistant. It is translucent unless dyes are added to color it or make it opaque...

)more expensive than paper. 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.

Callahan specifically recommended the use of Manila paper

Manila paper

Manila paper is a type of paper originally made from Manila hemp or abacá. It is buff in color and the fibers are usually visible to the naked eye. Because manila paper is generally inexpensive, it is commonly given to children for making child art....

, 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.

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

Telegraphy is the long-distance transmission of messages via some form of signalling technology. Telegraphy requires messages to be converted to a code which is known to both sender and receiver...

 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

Page header

A page header or simply header in typography is text which is separated from the main body of text and appears at the top of a printed page...

 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 mail

Mail

Mail, or post, is a system for transporting letters and other tangible objects: written documents, typically enclosed in envelopes, and also small packages are delivered to destinations around the world. Anything sent through the postal system is called mail or post.In principle, a postal service...

ings.