On the Surface – WearGuard Felt: GAMMA Championship Tennis Balls, now featuring WearGuard Felt with wear resistant fibers, are more durable and wear more evenly on all court surfaces, remaining more consistent and maintaining high playability longer than comparable championship balls. At the Core - Nitrogen: GAMMA Championship Tennis Balls are pressurized with Nitrogen to retain pressure longer and maintain a lively resilient bounce on all court surfaces. ITF and USTA approved. 24 Cans per case.