To transform a traditional gymball into an office chair, you need the Tunturi Anti-Burst Gymball Cover (14TUSFU196). The cover has an anti-roll function that stabilizes the ball and prevents it from rolling away when the user stands up. The material is machine-washable and can be easily slipped over the ball. A zipper closes the ball cover. Suitable only for Anti-Burst gymballs. The gymball must be purchased separately, but is also available in the online store. The ball cover fits a 75 cm diameter Anti-Burst gymnastic ball.