Neoprene
Also: neoprene suit, wetsuit
Neoprene is a foam rubber that keeps you warm when wet. Wetsuits are cheaper than dry suits but protect less well when paddling.
In a wetsuit you cool down through wind and evaporation as soon as you're wet. It's enough for warm water or short distances, but in cold water a dry suit is much safer. Neoprene shoes and gloves, on the other hand, are very popular.