a method of molding a plastic part with a controlled density whereby a blowing agent is added to a plastic material and the material is injected into a mold cavity of a mold unit . the interior walls of the mold cavity are maintained at a temperature sufficient to prevent the outer skin of the forming plastic article from producing gas bubbles . the volume of the mold cavity is increased to allow bubbles to produce and uniformly distribute themselves throughout the mold cavity and then a recompression phase is instituted whereby the desired density of the finished plastic article is achieved without voids or aberrations appearing in the surface of the plastic article .