note: we also carry the oncourt spinner balls, which are the same size as the gamma revolution. the oncourt spinners weigh slighly less (fraction of an ounce less)and do not bounce quite as high as the revolution balls, however the oncourt balls are about 6$ less in cost. please compare both, as to your needs and cost. ie. with younger children a lighter ball may be more desireable, although it won't bounce as high.. Gamma Revolution Balls are designed with beginners and accomplished players in mind. The oversized foam balls have a Magnacore which offers a bounce similiar to a standard tennis ball that makes an easier target for beginners. Accomplished players use them for warming up because it is easier on their arm and less effort when one begins play. 12 ball pack comes in a reusable polyester mesh carrying bag.