Huub Skull Cap The Huub Skull Cap is a fully adjustable swim hat. It has an adjustable strap for extra comfort when swimming in open water. Constructed using a high-grade neoprene, the Huub Skull Cap is designed to ensure comfort and warmth. Dubbed the most comfortable swim cap on the market, this neoprene cap sits comfortably against the head and ears to keep you warm in open water swims. The thick neoprene construction ensures added warmth in any cold water swim so you can continue with strength and speed. Completing the neoprene skull cap is a chin strap which can be adjusted to ensure a perfect fit.