The XLR8 balls were designed with a specific intent: How do we instruct baseball players to hit different speeds of pitches? Answer: Produce a ball that flies at different speeds! Obviously, one ball could not accomplish this without some manipulation by the “pitcher”. Not anymore. One XLR8 ball is slightly heavier and constructed of a different density of foam than the other. The differing weights and densities create different flight characteristics when thrown with the same arm speed. The heavier ball flies straighter and faster than the lighter ball. Presto! Instant off-speed pitch training without any manipulation from the “pitcher”. Now Mom, Dad, your sister or anyone else can throw great batting practice without any effort or knowledge about baseball. Simply throw the XLR8 balls and they do the rest. IN STOCK