The HART Slam Balls Complete Setballs are constructed with a strong outer rubber casing filled with special iron sand. Designed to not roll away or bounce when dropped, they are great for throwing and slamming exercises as well as all normal medicine ball activities. The pliable outer shell also adds variety when using the ball as a platform for floor-based exercises. 4, 6, 8, 10kg diameter: 23cm 12,15,20kg diameter: 25cm