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Gas-assisted injection molding, “GAIN”, is a thermoplastic molding process which provides stress-free large parts with a class “A” surface and vitually no sink marks. “GAIN” is a low-pressure molding process, compared to conventional injection molding. In this process, a controlled volume of inert gas is injected into the plastic after it enters the mold. The gas does not mix with the plastic, but remains in the middle of the thicker sections of the molding. By controlling the gas pressure, the quantity of plastic injected into the mold (short shot), and the rate of gas flow, a predetermined network of hollow interconnecting channels is formed within the molded part. The gas pressure remains constant in the network of hollow channels throughout the molding. This compensates for the tendency of the plastic to shrink at the thicker areas of molding, preventing warpage and reducing stress. The gas pressure is relieved just prior to opening the mold.