Abstract: Wood can be rendered fire resistant by impregnating the wood with a solution of a monomer, such as a phenol, and a fire-inhibiting salt, drying the wood and thereafter treating the wood with a solution of a second monomer, such as formaldehyde, polymerizable with the first monomer. Heating to dryness causes polymerization of the monomers. The fire resistant properties of wood treated this way are not affected by exposure to moisture. Prior to the first impregnation, after the first impregnation and after treatment with the second monomer the wood being treated is dried to a moisture content below about 4%.