Abstract: A thermoplastic article can be injection molded in a mold (10) which includes a cavity (28) defining the shape of the article, at least one thermoplastic entry aperture (23) which is adapted to receive molten thermoplastic resin from a nozzle (22) of an injection molding machine (24), a thermoplastic flow path (21, 26, 30) communicating with the thermoplastic entry aperture and the cavity, and a fluid flow passageway (32, 34) extending into the mold. The fluid flow passageway extends from an exterior surface of the mold to the thermoplastic flow path. A low viscosity fluid such as a gas can be injected through the fluid flow passageway and into the thermoplastic flow path. An end portion (44) of the fluid is flow passageway adjacent the thermoplastic flow path has a porous me lug (50) disposed therein. The porous metal plug includes a porous metal core (64) which permits the low viscosity fluid to flow therethrough but prevents the passage of molten plastic therethrough.