Slam Balls add a bit of cardio to your strength workout while releasing stress or an excess amount of energy. Built to take a slam, this sand filled ball lets you perform a wide range of ballistic core exercises. The sand allows the ball to absorb the energy of a slam instead of the ball bouncing or rolling away. Other look-alike slammer balls have seams that can split. Ours are a specially formulated resilient soft shell which is rotationally molded for a seamless construction. Perfect for crossfit slam ball, wood chops, overhead throws, twists. All Slam Balls have a 10" diameter. These premium balls are the choice of pro teams, crossfit studios, and military installations worldwide Non bounce No-roll construction Widely used in rehabilitatiion Strengthens the Core Available in 10, 15, 20, 25, 30 lb. All Balls are Black All Balls have 10" diameter Set of Four contains one each of 15, 20, 25, 30 lb. Set does not include the 10 lb. Ball