Force Fin Adjustable Slim Fin: Comfort and Safety- Integrated Comfort Instep cushions and comforms to your foot for maximum comfort and reduced cramping. Works the muscles of the whole leg for better cardiovascular conditioning. Speed- Unique V-shaped blade channels water naturally, maximizing propulsion and speed. Vortex Generators,(the bumps on the underside of the fin,) accelerate water flow and help you move! Blade: Polyurethane, stiffness 87/rebound 78. Foot Pocket: Comfort Instep included; brings buoyancy to neutral. Straps: Parachute webbing with marine-quality hook-and-loop (foot pocket); elastic Bungie with Comfort Heel pad. Colors: Bahamian Blue, Jet Black. Sizes: One size adjusts to most.