[Featured Materials]: The base of this tennis back trainer is made of plastic material, which is durable and wear-resistant, and the ball is made of imported natural rubber material, which is sturdy and durable. [Excellent Tennis Practice Tool]: Fill the base with water, and this tennis back trainer instantly becomes heavy enough to hold the unit in place, and very light when empty, so it can be easily stored and carried to practice your shots and improve your swing speed. [More Suitable for Tennis Lovers]: At 8.3" wide and 2.0" high, this tennis back trainer fits easily into a tennis bag and is a great teaching tool for tennis beginners and intermediate players. [Equipped with Rope]: The tennis ball with black rope is the perfect portable tennis training aid and easy to use, just hit the ball and it will come back to you, convenient and practical to buy and use with peace of mind.