This is a Dog Medium Tennis Balls for Medium Chuck It Launcher - 2 Balls (6cm Diameter). Chuckit!® Tennis Balls are made of high-quality materials and specifically designed for the game of fetch. Constructed of a natural rubber it features an extra-thick rubber core and durable material that floats in water. The bright colors provide improved visibility when playing with your dog and help to prevent the ball from being lost. Use alone, or with your Chuckit! Launcher