Used Seac Tekno with Air Release Valve Vent System, 5mm Neoprene Hoods,The Seac Tekno scuba diving hood is made of 5 mm Ultraflex neoprene and is ideal retaining heat and keeping the head warm. The "Air Release" vent system allows excess air to escape from the top of the hood, avoiding the formation of an air build up in the hood. The super elasticity of the Ultraflex neoprene allows you to easily wear the Seac Tekno hood. The neck is designed with a smooth material for greater grip between the hood and the diving suit.