AFFF works by creating a film that stays on top of the flammable liquid to suppress vapors and a foam substance that helps cooling, insulates and separates other ignition sources or hostile fire from reigniting the vapors. All these qualities combine to produce a "finished foam product."

AFFF also has a "self healing" capability. If the foam & film layer is disturbed, vapors can release again and be ignited but AFFF moves "back into position" to do its job (With limitations). This "self healing" can only occur if enough foam product is still available, the surface of the fuel is not being disturbed and is not on a vertical surface. If the flammable liquid is boiling, suppression will be far more difficult and fire volume may increase dramatically due to available fuel surface area.