Heavy Duty! Soft hitting sensation. Heavy Duty + Feeling This new ball is introduced to the Japanese market that enjoys a firm and soft feel. The core is made of high quality material that is as resilient and durable as a premium ball. The felt is highly durable and has a lot of artificial turf coats with sand that contain minimal pilling. This is an ITF (International Tennis Federation) certified ball that is perfect for practice balls but can also be used in international competitions.