A ski suit is a suit made to be worn over the rest of the clothes when skiing. A ski suit is made from wind- and water-resistant or water-proof fabric. It is usually made to keep the body warm, but the user often wears warm underwear too. It can also be used for alpine racing to improve aerodynamics. Ski suits made for speed skiing and alpine skiing might be very thin and skintight, adding as little air resistance as possible to the body. A ski suit can either be one-piece, in the form of a jumpsuit, or two-piece, in the form of a ski jacket and matching trousers, called salopettes.