The swim cap. Good at keeping hair out of your eyes, protecting your hair, helping to keep you warm, and sometimes making you a little more hydrodynamic. A swim cap could help keep water out of a swimmer's ear - which helps prevent swimmers' ear problems! Swim caps come in as many colors as you can think of, and are often customized by teams, countries or races. Water Polo swim caps are special, made of fabric with a strap that ties under the chin, and they have the players number and a set or ear protectors built in to the swim cap.