Oceanic USA Vortex V-16 Diving Fin Patented Nature's Wing Propeller Fin Technology with four material compounds for ultimate performance and light weight Semi-rigid battens and natural rubber flex channels precisely control the shape of the blade during the fin stroke to optimize power and reduce drag Ergonomically designed foot pocket accommodates virtually all foot sizes and boot styles Now includes Spring Heel Strap for streamlined comfort and easy on and off Easy on/off fin strap with thumb loop; 4 - 6 Men's US shoe sizes/5 - 7 Women's US shoe sizes