A swim cap, swimming cap or bathing cap, is a tightly fitted, skin-tight garment, commonly made from silicone, latex or lycra, worn on the head by recreational and competitive swimmers.

Caps are worn for various reasons. Some facilities require the wearing of swim caps, in order to protect filters from becoming clogged with loose hairs which fall from the head of swimmers who are not wearing a cap, or to ensure long loose hair does not get caught in equipment. Caps are also sometimes worn in an attempt to keep hair relatively dry or protect from chlorinated water, to keep the sun off the hair, and also, when a cap is worn with ear plugs, in order to keep water out of the ears. Competitive swim caps also reduce drag in the water caused by loose hair. During longer swimming sessions, a swim cap keeps the wearer's head warm. In some countries swimming caps are required before entering the swimming pool, this is often the case in Italy and Hungary.