A fire-retardant paint that slows the spread of flames. An intumescent coating, when touched by flames, swells to form a protective foam that is about 50 times as thick as the original paint layer (Harp 1981). The foam insulates the wall with millions of microscopic air cells. The coating not only slows the spread of the fire, but it also minimizes the production of smoke and toxic gases.
D.Harp, "Intumescent Paints" Technology & Conservation, 1/81, p.30-31.