Ball chair lets you sit on an unstable ball to help normalize spinal fluid diffusion and provide proper nourishment to help keep your spinal discs elastic and strong. Active sitting also leads to increased brain stimulation, alertness and learning ability. Backless design triggers core engagement that's necessary for health and postural benefits. Included risers raise the height of the base to accommodate anyone between 5' to 6-1/2' tall. Heavy-duty, anti-burst vinyl may be expanded from 50cm to 60cm to allow a custom fit to your office.