In this study, the effects of processing parameters on the cellular morphologies and mechanical properties of thermoplastic polyolefin (TPO) microcellular foams are investigated. Microcellular closed cell TPO foams were prepared using a two-stage batch process method. The microstructure of these foamed samples was controlled by carefully altering the processing parameters such as saturation pressure, foaming temperature, and foaming time. Foam morphologies were characterized in terms of the cell density, foam density, and average cell size. Elastic modulus, tensile strength, and elongation at break of the foamed TPO samples were measured for different cell morphologies. The findings show that the mechanical properties are significantly affected by the foaming parameters that varied with the cell morphologies. The experimental results can be used to predict the microstructure and mechanical properties of microcellular polymeric TPO foams prepared with different processing parameters. (C) 2008 Wiley Periodicals, Inc.