Thera-Band Soft Weights: These soft weighted balls promote functional grip strength and development. A single size ball supports one or two-hand activities. Comfortable and fun to hold. They follow the Thera-Band easy-recognition system of color-coding. There are six levels of progressive weights. Each ball comes with a professional instruction manual which provides many programming options. Designed for the following applications: Strengthening, Plyometrics, Balance Training, and Mobilization. Made of a PVC shell, with. steel and polypropylene pellets as filler. The plug is polyethylene.