How are tennis balls made?

Today’s tennis balls are made of a hollow, two-piece rubber shell filled with pressurized gas. The rubber shell is covered with felt made from nylon or wool. The International Tennis Federation states that tennis balls should be between 2 1/2 and 2 5/8 inches in diameter and weigh between 2 and 2 1/16 oz. The factory uses a design that hasn’t changed much…