a method for constructing a structural foam part . the method comprises three steps . step one calls for utilizing a rapid prototyping process to create a polymer mold . step two requires filling the polymer mold with a material . the last step calls for heating the polymer mold and the material to heat set the material and to remove the polymer mold thereby forming the structural foam part . more specifically , the rapid prototyping process may be stereolithography , and the structural foam part may have a varying density such that different mechanical properties exist in different sections of the structural foam part .