There are many types of envelopes used for different purposes. Envelopes have been used since 3000-3500 BC and were originally made of clay. Modern paper envelopes emerged in 1845. Envelopes are classified by shape, size, and intended use. Some common types include announcement envelopes for invitations, baronial envelopes with pointed flaps, booklet envelopes with side flaps, window envelopes with address windows, clasp envelopes with metal closures, commercial flap envelopes for machine insertion, catalog envelopes that open from the end, ticket envelopes for event tickets, policy envelopes for business and personal use, square flap envelopes for cards, and wallet envelopes with