This is the backless chair with an exercise ball base that helps to improve your posture by gently exercising your core muscles. The polyester mesh outer layer houses a 16" diam. exercise ball--the same kind used by personal trainers and gyms for core strengthening and balance exercises--that rests on top of five steel feet with a chrome finish, providing a stable sitting surface while performing office work or watching TV, yet it is buoyant enough to force your abdominal muscles to engage, providing a low-impact, almost imperceptible workout that helps with spinal alignment. The exercise ball's pressure can be adjusted with the included hand air-pump. Please specify Black, Light Blue, or Red. 23" H x 16" Diam. (5 lbs.)