Set the desired hardness - The Water-Air punching bag from Super Pro consists of 3 components: a robust outer shell, an inner layer filled with water and a cylinder in the centre that is filled with air. You fill the water layer yourself. The water is then distributed evenly, making the punch bag equally hard at every point. In addition, the water ensures optimum weight distribution so that it swings back and forth less during training. The punchbag absorbs punches and kicks well, which minimises injuries. - Advantages of the air-filled cylinder: - The air-filled cylinder in the centre makes it possible to adjust the degree of hardness individually. You can add or release air using the pump included in the scope of delivery. This ensures optimum handling. The harder you want the Super Pro Water-Air punching bag to be, the more air you need to pump in.