There are two ways that foam fire extinguishers function. They first put out the fire by bringing the temperature down because they are primarily water-based and have the same cooling effect as water extinguishers. In addition, they include “Aqueous Film Forming Foam” (this is why they are also known as AFF foam extinguishers). The foam from the extinguishers suppresses the fire and traps the flammable vapours inside. This keeps the fire from rekindling. Foam fire extinguishers can also put out fires caused by flammable liquids by putting a barrier between the surface of the liquid and the flames.