Wetsuits are made of neoprene, which contains tiny nitrogen bubbles inside the material. These bubbles form an insulating barrier between your body and the water, proving excellent thermal protection. A thin layer of water will enter between your wetsuit and your body at the beginning of your dive, which is quickly warmed to your body temperature. In order to keep you warm, a wetsuit must fit snugly, so that this warm water layer is not constantly flushed out by colder water.