The split blades of the Zip™ swim fin act like propellers, twisting independently during each stroke to a precise angle of attack that creates lift and thrust. With an open heel adjustable ankle strap and patented Nature's Wing® fin technology, the Zip significantly reduces ankle fatigue for fitness swimmers, allowing for a full-leg workout that can be sustained over longer periods of time for maximum and efficient aerobic benefit. Color: Black / gray and white / gray available.