Speedo Biofuse technology for maximum comfort and fit 100% Silicone for excellent comfort Strengthen leg muscles - added resistance increases the workload on your leg muscles which improves strength and endurance Increase workout speed - Training Fins add extra propulsion to the stroke, which increases speed with minimum effort leaving you free to ingrain correct technique. Develop ankle mobility - The increased surface created by the Training Fins forces ankle extension during kicking, which makes the kick more propulsive and efficient.