Tarpline's Adjustable Shock Cords with Safety Hooks are fast, safe and easy to use. No other shock cord adjusts as quick and easy and it does not slip. The shock cord is made of natural rubber and is coated with a polyester braiding with UV treatment. which means it will stand up to harmful sun rays longer than any other shock cord. The hooks are made from strong and durable glass reinforced plastic. Clip on loose and tension, no over stretching. Hippo Clip Compatible- Simply hook the safety strap through the holein the end of Hippo Swivel Clip to create the ultimate tarp tie down!!