Selected Materials The base of this tennis ball trainer is made of plastic material, which is durable and wearresistant, and the ball is made of imported natural rubber material, which is sturdy and durable. Ecellent Tennis Practice Tool Fill the base with water, and this tennis ball trainer will immediately become heavy enough to hold the device in place, and very light when empty, so it can be easily stored and transported to practice your shots and improve your swing speed. More Suitable for Tennis Lovers With a width of 8.3 and a height of 2.0 this tennis ball trainer easily fits in a tennis bag and is an ecellent 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.