These balls help effectively get rid of shoulder pain, neck pain, upper and lower back pain, hip and glute pain and stiffness, leg and knee pain, calf pain, ankle stiffness and Achilles problems, Sciatica, Disc issues, Muscle tension. Easy to use, just simply lean on the massage ball and use your own body weight and gravity to relieve muscle knots and tension. Perfect for use while sitting on any chair, laying in bed, on the floor, or on a yoga mat. Its material is silicone and size is Size: 2 1/2'' (Dia) X 5'' (L)