The wearer gets wet in a semi-dry suit but the water that enters is soon warmed up and does not readily leave the suit, so the wearer remains warm. The trapped layer of water does not add to the suit's insulating ability, and any water circulation past the seals still causes heat loss, but semi-dry suits are cheap and simple compared to dry suits, and do not fail catastrophically. They are made from thick Neoprene, which provides good thermal protection, but lose buoyancy and thermal protection as the trapped gas bubbles in the neoprene foam compress at depth.