An envelope is a common packaging item, usually made of thin, flat material. It is designed to contain a flat objects, 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 to make the envelope structure by folding the sheet sides around a central rectangular area. In this way, a rectangle-faced enclosure is formed with an arrangement of four flaps on the reverse side.
Envelopes are classified according to the following criteria:
International standard ISO 269 (since withdrawn) defined several standard of envelope sizes, which are designed to use with ISO 216 standard paper sizes:
|Format||Dimensions (Height × Length)||Suitable content format|
|DL/E65||110 × 220 mm||1⁄3 A4|
|C7/C6||81 × 162 mm||1⁄3 A5|
|C6||114 × 162 mm||A6 (or 1⁄2 A5 or 1⁄4 A4)|
|C6/C5||114 × 229 mm||1⁄3 A4|
|C5||162 × 229 mm||A5 (or 1⁄2 A4)|
|C4||229 × 324 mm||A4|
|C3||324 × 458 mm||A3|
|B6||125 × 176 mm||C6|
|B5||176 × 250 mm||C5|
|B4||250 × 353 mm||C4|
|E4||280 × 400 mm||B4|
The window in an envelope often made in the form of a rectangle with rounded corners, closed from the inside with a clear film and allows to see the contents partially (for example, the address). The window can be of any size and position, but it is usually located in the lower right corner and measures 90 × 45 mm. The distance from the edge of the window to the edge of the envelope is not less than 15 mm.
Depending on the location of the closing flap, envelopes are classified into two types: