The outer nylon sleeve covering helps to protect against wear, nicks and cuts, as well as from the tubing being overstretched. This product can be used to help build strength and long lean muscle. In addition, the handles were designed to be extremely comfortable to hold. The loop tubes use significantly thicker and higher-quality materials than all competitors on the market. These professional-grade tubes are built to last and maintain their elasticity over many years of training. It's typically used by athletes, coaches, personal trainers, physical therapists and other professionals who need the most advanced product.