A method of forming a hardened skin on a surface of a molded article. In an exemplary method, a formable material is mixed with a blowing agent to form a foam material (20). The foam material (20) is placed in a flow molding apparatus (10) such that the top surface of the foam material is in contact with the top mold (16) of the apparatus and the bottom surface of the foam material is in contact with the bottom mold (18) of the apparatus. In operation, an alternating dielectric field is applied across the foam material (20) to form the molded article. At the end of the molding cycle, the bottom surface of the foam material (20) remains under the decomposition temperature of the blowing agent so as to form a hardened skin on the molded article.