Aquasphere Zip Fin

"Build stronger legs with patented Nature's Wing fin technology. By eliminating ankle fatigue you?ll be able to have full-leg workouts sustained over longer periods of time for maximum and efficient aerobic benefit. The unique blade features specially engineered side rails, strategically aligned flex channels, and hydrodynamic stiffening battons that combine to make the Zip Fin the most comfortable and efficient fitness fin on the market. Black/Blue (BLK). Medium size 6.5-9.5, Large size 10-13. "