Balance disc promotes core stability, strengthens muscle tone, improves balance and body posture. Used as a wiggle seat to provide sensory input, and to help calm children that have a hard time sitting still. Ergonomic seating, relieves back pain and shoulder aches Balance cushion provides an unstable surface to exercise on, requiring you to use more muscles to stay balanced. Ships inflated, includes a pump for adjustments. Stability disc size: 13 inches / 33 cm diameter