A processing technology that facilitates quality injection molding without prior drying of polymer pellets has been proposed. The main idea is not to let the water evaporate to bubbles inside the mold. The polymer will be maintained hydrated as it was in the hopper of the injection molding machine throughout the entire molding processes by controlling the cavity pressure above the saturation pressure of water until solidified. In this work, the gas counter pressure (GCP) system has been designed and built to maintain the cavity pressure above the saturation pressure. The performance of the proposed method has been examined by checking the visual quality and the mechanical properties of the molded parts. The method has been tested with pellets of polymethyl methacrylate (PMMA), polycarbonate, polyethylene terephthalate, polybutylene terephthalate, and polyamide 66. The results show that the GCP prevents surface impairment incurred by the vapors without or with minor effects on the mechanical properties. Finally, the effects of energy saving has been examined by conducting the actual process for 1 day. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers