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. TUSAs industry leading 3 year warranty.