Great for swim training, the Aqua Sphere Adults' Zip VX Swim Training Fin features a soft rubber foot pocket for comfortable wear and a vortex channel in the fin blade to add thrust, increase efficiency and reduce ankle strain. The adjustable heel strap provides a secure fit. Features and Benefits Great for use during swim training Vortex channel in the fin blade adds thrust, increases efficiency and reduces ankle strain Soft rubber foot pocket for comfortable wear Adjustable heel strap provides a secure fit