The bumps and tacky surface of these sensory balls work together to make them one of the easiest balls to catch and hold. When fully inflated, the small plastic beads fill only 1/3 of the ball's chamber. When rolled or shaken, the beads provide audible feedback of the ball's movement. They also provide a deadening effect that, depending on the degree of inflation, can turn Roll-N-Rattle Sensory Balls into beanbags. Set of 6. Measures 4 inches each.