Cornstarch is a common ingredient that adds a bounce to a bouncy ball. When mixed with water, cornstarch creates a bouncy, flexible putty. Or, you can use a rubber band to add the bounce factor to a ball. When a rubber band is stretched and then released, and it will snap back to its original shape and bounce. And if you want something with a more rubber-like consistency, choose the ingredient combination of borax, glue, and food coloring. Just mix those ingredients together and you'll have a bouncy ball in no time that bounces up and down.