Foam cannons create a dramatic blanket of suds, while the traditional bucket wash remains the familiar hands-on method. Both can produce a clean vehicle, but they solve different parts of the washing process. The best choice depends on your equipment, available time, and how dirty the vehicle is. What a foam cannon does A foam cannon connects to a pressure washer and mixes car-wash soap with water and air. The resulting foam clings to the vehicle, helping loosen road film and