FitBALLŪ SeatingDisc 15" Iridescent blue. Polybag. This air-filled disc has a unique dome-shaped top that mimics the FitBALL exercise ball. One of the most versatile fitness and rehabilitation tools available, the FitBALL Seating Disc can be used as a standard balance disc or as an active sitting cushion. Junior size also available. FitBALL Pump recommended for full inflation/adjustment.