This to ensure the brains function during all conditions. That is why the colder it gets, the more heat you loose from the head by radiation, or even worse, by conduction in the water. You keep warmer with an effective hood. Waterproof H1 HOODS including the unique HAVS (Hood Air Venting System) is constructed with these scientific facts in mind. That is what we call Facing Reality.H1 HOOD 3/5mm with BIB. Sizes: S, M, L, XL XXL. This item is in the category "Sporting Goods\Scuba & Snorkelling\Hoods". The seller is "aquaventurers" and is located in this country: GB.