The H1 3/5mm hood features a 5mm double layered protection in critical heat loss areas and glide skin seals for the neck and face. Waterproof H1 5mm includes the unique HAVS (Hood Air Venting System) which uses one-way valves to vent annoying air buildup in the hood. 3D Shaped. Glide skin seal. HAVS system (Hood Air Venting System). I-Span super-stretch nylon. Bonded hi-quality nylon thread.