Bottom and side flaps form an envelope's body and are usually permanently bonded in the folding operation. Seal flap shapes vary widely among different styles of envelopes. The most common flap shapes are:

Bankers Flap
Used on commercial style envelopes to provide additional sealing area.

Extension Flap
Some filing and special purpose envelopes are constructed without a flap; rather, an extension of the face, neither gummed nor scored, is provided to assist inserting material into the envelope.

Hub flap
Used on catalogs.

Pointed flap
Used on most baronials.

Round Flap
Used on some small coin, drug and pay envelopes.

Square Flap
Used on some announcements and some commercials.

Standard Flap
Used on commercial and some baronials.

Wallet Flap
Used on dual purpose, some commercials, collections, and order form envelopes, they provide additional area for printing on both the back and seal flap.