Maxafe® Sitsolution Balls have stability legs and are made from the best materials. A healthy and effective alternative to a traditional chair, it promotes good posture and core strength. If accidentally damaged by small cuts or punctures, the ball deflates slowly for added safety during use. The Legs help prevent these balls from rolling around when not in use. Available in 2 sizes: 21" (53cm) dia. or 26" (65cm) dia.