Airless tires, non-pneumatic tires (NPT), or flat-free tires are tires that are not supported by air pressure.[1][2][3] They can be used on small vehicles such as ride-on lawn mowers and motorized golf carts. They also are used on heavy equipment required to operate on sites where risk of tire punctures is high. Tires composed of closed-cell polyurethane foam are also made for bicycles and wheelchairs.[4]