Its purpose is to keep the hair close to the head and prevent hair from falling into the water. The cap creates less resistance and makes it easier for the swimmer to move forward. In winter, it helps to keep the head warm.

The cap does not keep the hair dry, but it limits contact with water and protects the hair from chlorinated water.
Silicone caps have an advantage because they are elastic and safe. They are economical and do not require special care after each training session.