Envelope is a common type of packaging which is usually made of thin, flat (mainly paper) material, designed to contain a flat and thin object (such as a letter or a card, but mainly for sending letter). Traditional envelopes are made from cutting-paper sheets to one of three shapes: rhombus, hand-crossed shape, or a kite. These shapes allow the creation of an envelope structure by folding two plates around a rectangular central area.

Envelopes also serve as a means to protect and secure mail (envelopes are usually sealed) and also have a shipping function.
With the need to exchange work and information today. It's important to design and print a company-specific envelope for branding. Here are some standard size samples of corporate brand identity products:
1. Standard small-size envelope: 12cm x 22cm
2. A5 paper containing envelope size with 2 types: big A5 type: 18cm x 24cm and normal type: 16 x 23cm (usually used for containing A5 paper).

3. Envelope size for containing A4 paper (often called A4 envelope): 25x34cm (often used for containing A4 paper, documents).