The very first BURLY CAPS were hand-crafted from natural white UHMW (Ultra-High Molecular Weight) polyethylene back in 1988. They continue this dedication to skateboarder's knees 25 years later. Thier plastic is significantly more durable than any of the injection-molded caps offered with most brands of knee pads. BURLY CAPS slide excellently on smooth concrete, skatelite, masonite, and birch ply, and will last years for most users. BURLY CAPS are the highest quality replacement caps for skateboard knee pads, they will outlast your knee pads, and maybe even your knees.