A method of making foamed articles that includes providing a copolymer composition, combining the copolymer composition and cellulosic fibers, applying heat, mixing energy and pressure to the copolymer composition and cellulosic fibers mixture to form a foamable mixture, and forming the foamed article by placing the foamable mixture in a molding or extruding operation. The copolymer composition includes a copolymer of 51% to 99.9% of primary monomers, 0.1% to 49% of anhydride containing monomers, and 0% to 25% of other monomers and 0% to 30% of elastomeric polymers. This is combined at 30% to 99.99% copolymer composition with 0.01% to 70% by cellulosic fibers such that the copolymer anhydride groups react with the cellulosic fiber hydroxyl groups to produce a blowing agent byproduct to form a foamable mixture. The foamed article has a density of not more than 1.3 g/cm3.