Abstract: Improve ASTM E-84 flame spread index and smoke developed index ratings of polyisocyanurate or urethane-modified isocyanurate foams by coating one or both major planar surfaces of a foam body or board with an intumescent coating material that contains expandable graphite and a silicate. If desired, provide reinforcement for the intumescent coating when it intumesces using a material such as a carbon veil mat or a fiberglass mat. Add a moisture vapor barrier layer to minimize water-induced degradation or water absorption of the foam.