The unpredictable bounce of these rubber balls forces athletes to make split-second decisions in order to catch the balls. The random bounce helps train reaction time and hand-eye coordination, so athletes improve overall coordination and depth perception. Throw the balls against any hard surface for multidimensional drills.2 Sizes! 4" Jumbo Reflex Ballå» has a softer bounce and larger size making it easier to catch. 3" Reflex Ball has a compact design producing faster, more erratic bounces. Dense rubber.