14 inch diameter, Black. The inflatable vestibular disc mimics both the movement and shape of the inflatable ball when used on any seat. It acts as a dynamic cushion to activate major muscle groups. Use it on the floor as a standing disc for balance training, proprioception, and strengthening of the lower extremities. Can be deflated to 1 thickness (mushy) or inflated to 2 thickness (firm). Each disc has one nubby side for tactile feedback and stimulation, and one flat side. Also available in 24" diameter.