Sharkskin Chillproof Hood for Scuba Diving and Watersports Sharkskin Chillproof is an aquatic specific, windproof 3-layer composite material that has been developed for water sports athletes. Hood fits close to the head to insulate in cool water Bibbed lower section tucks into wetsuit collar to reduce water flow Choose size based on forehead circumference S (20), M (21), L (22), XL (23), 2XL (24), 3XL (25), 4XL (26)