Rash guard are primarily used in warm water as a substitute for wetsuits, but are also often layered underneath wetsuits for comfort. Most are constructed of blends of Lycra, nylon, spandex, and/or polyester; they therefore don’t provide much warmth but offer excellent sun protection, keep sticky surf wax off your skin, help prevent chafing from your board. They can also protect you from scrapes against coral or stings from jellyfish.