Sandwich structures provide high stiffness at low weight and the use of polyurethane foam core has provided a versatile material for some time. Polyurethane duromer is the name of a new material which can produce a strong structural sandwich composite molding with integral solid urethane skins and a microporous core. Skins and core are produced simultaneously in a single operation from identical raw materials. The process is similar to injection molding, at relatively lower costs. These factors may provide the impetus to efforts directed toward making automotive body panels of plastic in economical mass production.