![]() ![]() ![]() 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. Ĭallahan specifically recommended the use of Manila paper, which is considerably cheaper than thicker writing paper and also provides an opaque background for secure covering of the letter within. The United States patent number for Callahan's design is 701,839. The design and patent letter were completed on 15 November 1901, with the patent filing occurring on 9 December 1901. The design has otherwise remained nearly unchanged. That material was soon replaced by glassine and by the end of the century, clear plastics some uses omit the film entirely, leaving an open cut-out. Originally called the "outlook envelop", the patent initially anticipated using thin rice paper as the transparent material forming the window. ![]() Callahan of Chicago, Illinois, in the United States, received the first patent for a windowed envelope on 10 June 1902. US Patent 701,839 for a windowed envelope Modern envelope with a single window for the recipient addressĪ windowed envelope is a conventional envelope with a transparent (typically PET or BOPS Bi-oriented polystyrene plastic film) window to allow the recipient's address to be printed on the paper contained within.Īmericus F. ![]()
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