advanced Resistance Zip System can be easily adjusted to different levels of intensity to take strength and endurance training to the next level. Features Adjustable Belt: Wide belt evenly distributes pressure for optimal comfort. Towline Buoy: Maintains proper body alignment without interrupting a natural kick cycle. Marine-Grade Chute: Durable, hydrodynamic design allows water to flow through at maximum speeds. Resistance Zip System: Industrial-grade zippers and resistance indicators allow for customized intensity. Build Strength and Power: Increased intensity places more demand on key muscle groups and builds aerobic endurance. Variable Resistance: Advanced Resistance Zip System allows for variable levels of resistance specific to swim stroke and distance. Boost Speed: When resistance is removed, speed and stroke rate can be increased. Various Users: Applicable for fitness swimmers, competitive athletes, and triathletes. Details Material: Marine-Grade Polyester. One size fits all. Designed for swimmers age 14 . CAUTION: For use by competent swimmers only. Drag Fly is NOT a flotation device.