Features: Made of high-quality PVC material, lightweight and durable, no easy to deform. Bottom chamber is for water or sand to increase weight to keep it stand stable on the ground, more stable and reliable. Upper chamber is for inflating air to avoid scratching the skin of your limbs, soft and elastic. The resilient backbone for better stability, bounce back up immediately without falling over. Great accessory for improving coordination and flexibility, burning calories and relieve pressure, suitable for kids, teens, and adults.