Slam Ball PRO 5kg Medicine Ball 100422 Properties: The ball is used during intense CrossFit training. It's made entirely of rubber, making it much better and more practical than leather versions, which often have seams that break. The ball is waterproof, so it can also be used outdoors. material: rubber filling: synthetic sand weight: 5 kg diameter approx. 23-24 cm circumference approx. 75-76cm