Apollo Bio-fin Xt Open Heel Scuba Split Fins with Rubber Straps Increasing the durometer to 75 rather than changing base material creates a stiffer blade that retains a high degree of the comfort and performance of our original bio-fin pro Higher durometer rubber provides the feel and weight of a more traditional fin Works as well or better than paddle fins with any choice of kicking style Split fin design allows for increased maximum speed and reduced fatigue Consistently rated as the fastest fin in the water