These balls are felted from 100% wool, so they are chemical-free and safe for a cat that bites and carries its toys. The felt gives them a soft, satisfying weight that skitters across a floor when swatted and holds up to claws better than the throwaway foam kind.Sold as a set of three colors, so there is always one in play after the others vanish under the furniture. The 4cm size suits batting and carrying.