The Body Sport Balance Disc is similar in movement and shape to a fitness ball when used on any seat. Can be used as a dynamic cushion to activate major muscle groups, or as a standing disc for balance training and lower extremity strengthening. Features one tactile side and one smooth side. Inflates with a standard pump (not included). Can be deflated to 1″ thickness, or inflated to 2″ thickness. 13.8″ (35-cm) diameter.