Abstract : Formulation studies using commercial Saran microspheres and halogenated latex binder led to the development of aqueous intumescent coatings. When modified with certain flame retardant additives, compositions impart excellent flame spread resistance to wood substrates. Microsphere/latex compositions modified with decabromodiphenyl oxide provide good flame insulation properties for steel panels; panel backside temperatures remained below 1000 F during flame exposure of phosphatized steel panels coated with intumescent composition. Latex/microsphere intumescent coatings show good quality and appearance when applied to wood. Further work on primer systems is needed, however, to eliminate cracking and discoloration of coatings when applied to steel panels.