Envelopes and Bags of various sizes
The coding for envelope sizes follows that of the paper sizes. A bundle of A4 sheets of paper will fit into a C4 envelope. A C5 envelope will take a bundle of A4 sheets that have been folded into halves. An A4 sheet folded twice, into quarters, will fit into a C6 envelope, as will a C6 greetings card, or some postcards.
Envelopes also come in various styles. Greetings card envelopes normally have a diagonal, and gummed, flap. Their paper weight is frequently 80gsm. Correspondence cards need a straight flap and a substantial weight of paper, normally 100 or 120gsm. Office envelopes come in all sorts. Traditionally
C5 envelopes
C6 envelopes
Sized to take A6 paper (appx 6x4 inches)
Polypropylene 'Crystal' bags
Clear plastic bags for protecting and displaying envelopes
Speciality envelopes
Envelopes using special papers
White business envelopes
White envelopes suitable for business use
White greetings card envelopes
Diagonal flap gummed envelopes in standard sizes