A microcellular foam was prepared from a thermoplastic elastomer by a batch physical foaming with CO2. Two hydrogenated polystyrene-b-polybutadiene-b-polystyrene (SEBS) copolymers with different styrene ratios were used as an elastomer basis and blended with polystyrene (PS) to control their rigidity and gas permeability. The end-blocks of the SEBS form a physical cross-link and provide a rubber-like elasticity when cooled. SEBS alone, with its lower styrene content, cannot be physically foamed while retaining a stable-shape dimension because of its higher gas permeability and lower rigidity. SEBS with higher styrene contents were used, or the PS blend ratio was increased to 80/20 or 50/50, and batch physical foaming experiments were conducted at three temperature levels (60, 100, and 120 degrees C) while the sorption CO2 pressure was maintained at 10 MPa. Increasing the styrene content or blending PS with SEBS increased the storage modulus and decreased the gas permeability. As a result, the shrinkage of the foam was controlled, and stable microcellular elastomer foams could be prepared. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013