This is the 4th Element 3mm Rock Hopper Dive Boot with Ergonomic Footbed Features: 100% natural rubber outer 88% recycled lining Ergonomic footbed insoles Heel reinforcement Fin strap retainer Smoothskin ankle seal The Rock Hopper shoes are lightweight yet pack a punch in comfort and versatility. Comfortable for clambering over rocks thanks to the natural rubber outsole and ergonomic footbed, the Rock Hoppers are equally suited to use with open heel fins thanks to heel reinforcement and a durable lining over the bridge of the foot. OceanPositive: The 3mm stretch neoprene is very comfortable and is lined with OceanPositive fabric made from recycled plastic bottles. The smoothskin seal around the ankle minimises water movement and helps to keep the shoes in place whether walking, climbing or finning.