Bum flap

[1] In another usage (train hopping), the term refers to a piece of removable material that hangs from the waist to cover a person's buttocks.

[citation needed] Sitting or sliding on a rough surface can rapidly wear the seat of pants, and flaps act as replaceable buffer material.

Bum flaps are often worn as a superfluous fashion statement, usually emblazoned with punk iconography.

Flaps are usually constructed by hand with the most suitable material available, often canvas or denim from discarded clothing.

Water resistant and thermally insulating flaps are desirable for long distance freighthopping rail travel and camping.