- to carry your messages in style...
An envelope is a packaging product, usually made of flat material such as paper or cardboard, and designed to contain a flat object, which in a postal-service context is usually a letter, card or bills. The traditional type is made from a sheet of paper cut to one of three shapes: the rhombus (also referred to as a lozenge or diamond), the short-arm cross, and the kite. These designs ensure that in the course of envelope manufacture when the sides of the sheet are folded about a delineated central rectangular area, a rectangular-faced, usually oblong, enclosure is formed with an arrangement of four flaps on the reverse side, which, by virtue of the shapes of sheet traditionally used, is inevitably symmetrical.
Window envelopes have a hole cut in the front side that allows the paper within to be seen. They are generally arranged so that the sending address printed on the letter is visible, saving the sender from having to duplicate the address on the envelope itself. The window is normally covered with a transparent or translucent film to protect the letter inside.
According to international postal conventions, a letter envelope must measure at least 90 × 140 mm. The length of postcards and aerograms must be at least the width times the square root of 2. These requirements help sorting letters by making it easier to line up all the envelopes with the addresses reading the same way.
The same regulations also reserve certain regions on the envelope for the address, the postage, as well as markings that can be added by sorting machines.
In some countries using postcodes, common envelopes are preprinted with lines and boxes that help write those postcodes in a consistent way in a consistent position.