The Edge fins are designed to improve technique and give your legs a real workout. It takes power to push these fins through the water, which results in building strength and endurance. The side rails on the fin activate your hips and quadriceps ? enforcing a proper kick that starts at your hips and not your knees. This motion is great for glute and hamstring development. Made of 100% silicone, Edge fins will mold to your feet over time, like breaking in a new pair of shoes.