| An envelope is a packaging product, usually made | | | | its name. |
| of flat, planar material such as paper or | | | | According to international postal conventions, a |
| cardboard, and designed to contain a flat object, | | | | letter envelope must measure at least 90 × |
| which in a postal-service context is usually a | | | | 140 mm. The length of postcards and aerograms |
| letter, card or bills. The traditional type is made | | | | must be at least the width times the square root |
| from a sheet of paper cut to one of three | | | | of 2. These requirements help sorting letters by |
| shapes: the rhombus (also referred to as a | | | | making it easier to line up all the envelopes with |
| lozenge or diamond), the short-arm cross, and the | | | | the addresses reading the same way. |
| kite. These designs ensure that in the course of | | | | The same regulations also reserve certain regions |
| envelope manufacture when the sides of the | | | | on the envelope for the address, the postage, as |
| sheet are folded about a delineated central | | | | well as markings that can be added by sorting |
| rectangular area, a rectangular-faced, usually | | | | machines. |
| oblong, enclosure is formed with an arrangement | | | | In some countries using postcodes, common |
| of four flaps on the reverse side, which, by virtue | | | | envelopes are preprinted with lines and boxes that |
| of the shapes of sheet traditionally used, is | | | | help write those postcodes in a consistent way in |
| inevitably symmetrical. | | | | a consistent position. |
| In 1876 William Irwin Martin published the | | | | Padded envelopes where introduced to give extra |
| Stationer's Handbook. He worked for the Samuel | | | | protection to more dilicate items sent through the |
| Raynor & Company in New York. He created | | | | post. Jiffy padded envelopes are made from a |
| the first commercial sizes of envelopes and simply | | | | strong high quality punture and tear resistant |
| numbered them from 0 through 12. It was mostly | | | | kraft paper and filled with re-cycled paper fibres |
| for social and business stationery purposes in | | | | for maximum cushioning. |
| those days. That's how the No. 10 envelope got | | | | |