Foam is a mixture of foam concentrate, water, and air that forms a blanket of bubbles over the surface of the flammable liquid thereby suppressing the release of flammable vapors, separating the vapors from the air necessary for combustion; and cooling the fuel and hot surfaces.

Marine foam systems comprise a system distribution control valve, a tank, a foam proportioner, a pumped seawater supply distribution pipework, and discharge devices such as nozzles, branch pipes, and monitors. Water and foam concentrate are fed to the proportioner, which meters the foam concentrate into the water at a predetermined rate, usually 3% (3 parts foam concentrate to 97 parts water). This “foam solution” flows through the distribution pipework to the discharge devices, which mix air into the foam solution (aspirate) to deliver foam onto the fire.