Imagine a tall giant standing at 20m tall weights 40 metric tonnes, they have been watching us playing table tennis and were hoping that one day they could play too. How do I design a giant ping pong ball for these giants? What material would the ball be made of?
I'd use the same synthetic rubber, fabric, and wire combination used in vehicle tires. It needs to bear its own weight without breaking on impact, have the necessary elasticity to create a satisfactory bounce, and enough mass to overcome wind resistance at the larger size so you can achieve a solid forward trajectory after each hit. Something too bouncy (like dodgeballs) would be utter chaos.
Equally large (ha ha) problems would include the size and composition of the table and paddles...