We investigated the effect of polydimethylsiloxane (PDMS) on the foaming properties of block-copolymerized polypropylene (B-PP) by blending different contents of PDMS with B-PP in the extrusion process using supercritical CO2 as the blowing agent. The experimental results indicate that the addition of PDMS greatly increased the expansion ratio of the foamed samples. At the same time, the cell population density of foams obtained from the blends also increased to a certain degree and provided a new perspective on improving B-PP's foaming performance. The addition of PDMS also decreased the die pressure because of the reduced viscosity of the B-PP/PDMS blends compared with that of the B-PP matrix. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012