Certain foams can be used to fill tires. By filling the tires with foam, you protect the tire from going flat. It keeps the pressure at a static point so you do not suffer uneven wearing of the surface of the tire. If the tire is punctured, nothing can escape, so the tire is just as useful as it was before. This type of filling is popular in vehicles that go over many terrains, such as golf carts, tractors and mowers.
Most foam for tires is made of polyurethane. This is considered "ultra-lite." This is considered helpful, as it does not add extra wear to the axle or engine. The heavier the tire is, the harder it is to turn. That can cause the engine to work harder, as well as the machine to go through more fuel on a regular basis. This type of foam can be put inside any type of tire via injection.
Another type of foam is elastomeric. This foaming process requires curing with a "tire carcass." The carcase interior is placed under high atmospheric pressure. The foam is injected and stabilises the unstable super-pressurised cells of the surface. The foam only fills halfway, as once the tire is depressurised, the foam will fill the rest of the space. Elastomeric foam is made up of mostly silicon.
The "foam" is made by injecting two chemicals into the tire that when combined, produce a solid foam strong enough for tires, but not much more in weight than air. One of the compounds is lightweight urethane. Different foaming products use different chemicals as the catalyst, but they are all hydroxyl in nature. This means they are a form of alcohol. By mixing this with the urethane, the product builds on itself, creating the "foam." The byproduct of "foaming" is large amounts of carbon dioxide, so it should be done in well-ventilated areas.