It has two compartments. The bottom one is for water or sand to add weight to keep it stable on the ground. The upper is for air so you can train your skills. The base can be filled with sand or water for stability. Sand has been shown to be more effective in older children. Durable vinyl construction withstands impact and keeps bouncing forward.MULTIFUNCTIONAL: This fun inflatable punching bag is for fitness and stress relief. Improve coordination and flexibility, burn Burn calories and reduce stress while improving mobility and hand-eye coordination. The back and forth swing on each punch is also great for kickboxing workouts. Available for adults and children. Lightweight and Durable: This target is made of premium PVC material, which is lightweight and durable, with a thickened bottom design for portability. The hanging design of the durable bag allows you to move to where it matters most most comfortable - for your home or commercial gym. Fitness punching bag: fun for the whole family. Easy to inflate and deflate, folds small for easy storage. This boxing ring trains coordination and reflexes - losing weight is fun - and no more sweating in the gym. Eliminate stress and depression. Practical, safe and ideal as a boxing trainer for children as there is no risk of injury.