Harrow Pickleball Indoor Balls feature a seamless design for durability and consistent play. 12 pack. USAPA Approved. Pickle-ball was invented in 1965 and is typically played on a badminton-sized court with special paddles made of wood or high-tech aerospace materials while the ball is similar to a wiffle ball, but slightly smaller. Pickleball balls are made through a rotationally molded one-piece construction process. Once the balls cool down, holes are then drilled into the balls. Indoor pickleball is played on wood or tile floor while outdoor balls have a thick wall construction for increased durability since the game takes place on clay or sand like surfaces. Because the surface is much smoother, indoor balls move much faster. The larger holes in the ball are there to slow down the ball so that the game can enjoyed by all.