AFFF Station No. 5 & 6 (3-144-2-Q). AFFF (aqueous film-forming foam) is a synthetic foam with low viscosity that spreads rapidly across the surface of most hydrocarbon fuels and rapidly extinguishes fuel fires. It has the additional property of forming an aqueous film on the fuel surface that prevents evaporation and hence, reignition of the fuel once it has been extinguished by the foam.