The Oceanic Manta Ray Open Heel Fins, inspired by nature, three advanced materials simulate the shape & mechanics of marine animals. Fin blades are made from techno-polymer advanced material that provides the strength of bone to maximize power, speed & efficiency, while being extremely lightweight & durable. Oceanic's Power-X System is a revolutionary material that acts as tendon & joint, optimizing propulsion by flexing during the down-stroke and releasing stored energy prior to the upstroke. Unique positioning allows the Power-X System to deliver maximum power to the blade while evenly distributing pressure over the foot to minimize fatigue. Blades have power channels that are flexible material simulates the elasticity of skin by directing water flow off the back of the blade for increased thrust. Inspired by aircraft technology, winglets along the length of the blade increase efficiency and improve maneuverability. Fins come equipped with soft-pad heel spring straps that have an ergonomic finger-loop which allows the fin to be easily removed & replaced, even with thick neoprene gloves. Easy buckle adjustment (EBA) allows for more than 2" (5 cm) of precise adjustments for a custom fit without tools. Easy to use spring straps automatically compensates for different size feet and boots. Spring fin straps are depth compensating because they will compress to changes in the thickness of your boots.