This system automatically add more air to the tyre as it moves. This reduces the need to pump up tyres on a regular basis as they go down. Air is drawn in from the atmosphere through a one-way valve, which sits in the valve stem. Instead of going directly into the inner tube, however, the air goes into one end of the tube-like pumping mechanism, which runs along the outside perimeter of the main inner tube. As the tire rolls against the ground, the pumping mechanism is compressed, forcing air into the inner tube. The resulting absence of air in the pumping mechanism creates a vacuum effect, drawing more air in through the valve. If the inner tube is already at its desired pressure (which can be set on a dial on the valve stem), no additional air is pulled in. (Source Gizmag. Dec 14 2015. http://www.gizmag.com/pumptube-self-inflating-inner-tube/40902/)