The UF 21 fins have an advanced multi flex long blade design thrust channel technology for superior propulsion and the foot pocket is made with a soft durable compound designed for comfort The open heel design allows for quick and easy size adjustment and the silicone heel strap enhances comfort and durability This fin is engineered to provide a lot of power for its compact size The fins are lightweight and ideal for travel TUSA TMs industry leading 3 year warranty Features Advanced Multi Flex long blade design Thrust Channel Technology Maximum propulsion and comfort Soft comfortable open heel foot pocket with adjustable silicone strap Designed for ease of entry yet secure fit