Envelope

Stationery item used for flat mail Front of an envelope mailed in the U.S. in 1906, with a postage stamp and address Back of the above envelope, showing an additional receiving post office postmark 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 short-arm cross or a kite. These shapes allow the envelope structure to be made by folding the sheet sides around a central rectangular area. In this manner, a rectangle-faced enclosure is formed with an arrangement of four flaps on the reverse side. Overview Patent drawing of Americus Callahan's windowed envelope A folding sequence such that the last flap closed is on a short side is referred to in commercial envelope manufacture as a pocket – a format frequently employed in the packaging of small quantities of seeds. Although in principle the flaps can be held in place by securing the topmost flap at a single point (for example with a wax seal), generally they are pasted or gummed together at the overlaps. They are most commonly used for enclosing and