Orientation in injection molded polypropylene tensile bars was examined by microscopic and infrared dichroism. methods. These methods were then applied to tensile bars molded from TPOs. The injection molded parts were shown to have up to five distinct layers of varying orientation between the outer edge and the center of the sample. In both the polypropylene and TPO formulations, the skin thickness of the moldings increased as the polymer molecular weight increased. A unique, highly oriented region occurred in the core of TPO samples, in contrast to the reduced orientation observed in parts made of propylene homopolymer. The visual observations made from optical photomicrographs were successfully correlated with quantitative orientation data determined by infrared microspectroscopy. (C) 2004 Society of Plastics Engineers.