Tusa Imprex Open Heel Fins (SF-8800 or SF-7700 or SF-9900) updated

The IMPREX fin blade itself is made of different materials. The outside ribs are made from stiff material and between the ribs you'll find softer, more pliable material. The middle ribs are more compliant than the outer ribs which allows the fin to effectively channel the water while you swim, similar to the whip-like motions of the dolphin.