Zone 3 Neoprene Swim Cap This Zone 3 Neoprene Swim Cap offers great thermal protection when in the water and the best possible fit. Constructed using a high-quality 4mm Yamamoto Smoothskin material, this Zone 3 Swim Cap provides warmth whilst still maintaining good hydrodynamics through the water. Designed to give the best fit possible, the cap features a Velcro strap that joins under the chin to suit different head sizes. This design helps to alleviate the tight feeling under the chin, which is common with one-piece caps, thanks to its adjustability.