The FINIS Edge fins are the ultimate speed training fins and have been engineered to do it all. Through rigourous testing at the FINIS Stroke Lab, the Edge fins have been designed to optimize training without disturbing the natural kick cycle while providing excellent comfort. The combination of an 100% silicone based material and FINIS trademarked SmartFin™ Technology allowing for a proper kick at high speeds, builds cardiovascular endurance and activates key muscle groups for a more powerful up-kick. Features SmartFin™ Technology- Combination of blade angle and hydrodynamic vents for a natural kick cycle with powerful forward propulsion. Technically Advanced Speed - Increased surface area and reinforced side rails for a proper kick and high speeds. Industry-Leading Comfort - Ergonomic contours maintain constant connection witht he top of the foot to prvent skin iiitation and tension. Targets Key Muscle Groups - Designed to catch water on the up-kick, activating hamstrings and glutes. Proprietary Blade Angle - Designed to feel like a natural extension of the foot. High-Performance Vents - Advanced vent system redirects water flow, eliminating drag and increasing propulsive forces. Open Heel and Toe Design - Increases range of motion, open toe space for the most comfortable fit. 100% Silicone - Optimum performance and comfort. Size Identification - Color swatch on the bottom of the fin indicates respective size: Small (Blue), Medium (Green), Large (Red), XL, (Black). User Tip - The Edge fins are designed with a slightly narrow foot pocket to provide a snug and secure fit. Users with a wide or long arched foot may prefer a size up.