A method of forming a hardened skin on one or more surfaces of a molded article. In an exemplary method, a formable material is mixed with a blowing agent to form a foam material. The foam material is placed in a flow molding apparatus such that a first surface of the foam material is in contact with a first mold section and a second surface of the foam material is in contact with a second mold section. In operation, an alternating dielectric field is applied across the foam material to form the molded article. At the end of the molding cycle, the first and/or second surfaces of the foam material remain under the decomposition temperature of the blowing agent and are not blown so as to form one or more thicknesses of hardened skin on the molded article.