An intumescent polyurethane flame-retardant coating, blended respectively with (carbamide,) dicyandiamide or a compound of carbamide and dicyandiamide as a foaming agent, was applied to plywood. Heat release rates for combustion of the coated plywood samples were tested according to FAA standards. Compared with plywood control specimens, the coated samples showed better flame retardancy. Among the three foaming agents, the compound of carbamide and dicyandiamide revealed the most effective results in retarding plywood combustion.