The Gaiam(R) Balance Ball Chair provides all-day ergonomic support for a stronger healthier back. By sitting on the ball, you'll improve your posture and spinal alignment while getting a powerful core-strengthening workout. Improve Your Core Strengthens your core as you sit Easy one-tool assembly With anti-burst, 52cm Balance Ball Stable, yet lightweight base is made from molded PVC Designed for heights of 5'-5'11" and weights up to 300 lbs.