14in/35cm in diameter, large spiky dimples on one side (for standing), very small dimples on the reverse side (for sitting).
Durable & safe: Helps improve balance, coordination and flexibility; Good for active sitting, muscle strengthening, and joint stabilization.
Instruction: To inflate, the pin from the pump must break through the valve to reach inside of the cushion, or the pin hole would be BLOCKED by the valve wall preventing air to enter. To release the air from the cushion, just insert the pin without the barrel of the pump. Find the valve in the cushion on the 4th outer ring--one spiky dimple is replaced by the valve inside of a small hole.