Latex rubber and silicone swim caps, when properly worn, will help keep your hair dry. Thus, your hair, because it won't get wet, will also be protected from exposure to the chlorine in the pool water. This is an extra bonus for those with permed or color-treated hair, which is especially vulnerable to damage from chlorine in pool water. Lycra swim caps are not designed to keep your hair dry, so they do not provide the same protection against chlorine.
Because they keep your hair and head dry, latex rubber and silicone swim caps also offer some insulation, preventing heat loss through the head. While you're unlikely to carry a swim cap as survival gear in case of a boating or fishing accident, this extra insulation may be of value to recreational swimmers in cold, outdoor water or to those who are uncomfortable in cold swimming pools.
A swim cap, properly fitted so that it is snug to the head, will reduce hydrodynamic drag. This advantage is, for obvious reasons, of particular interest to competitive swimmers interested in shaving fractions of a second off their times.
No Clogged Drains
Swim caps, even Lycra caps that aren't waterproof, serve to keep long hair out of your eyes, offering vital protection for swimmers who don't wear goggles. They also keep that same hair out of the swimming pool's drain and filter system. At one time swim caps were mandatory for women in public swimming pools, although this is no longer the case in most places. If you're worried about losing hair, steer clear of rubber swim caps, as they are known for getting tangled in long hair; use a silicone or Lycra cap instead.