Non-pneumatic tires (NPT), or Airless tires, are tires that are not supporte by air pressure. They are used on some small vehicles such as riding lawn mowers and motorized golf carts. Tires composed of closed-cell polyurethane foam are also made for bicycles and wheelchairs. The main advantage of airless tires is that they cannot go flat, but they are far less common than airfilled tires.