The Lycra/nylon LOOSE FIT rash guard is designed to fit loose, similar to a T-shirt. It provides excellent UV, rash and jellyfish protection. These shirts are a great first layer under wetsuits or a great stand alone shirt for the beach, lake or pool. Order the same size as your wear in a t-shirt for a loose type fit. For layering under a wetsuit, we recommend going down one full size from your normal t-shirt size.