Linear polypropylene (PP) foams, blown in the continuous extrusion process using supercritical CO2 as the blowing agent, exhibited poor cell morphology and narrow foaming window, because of their low melt strength. In this study, polytetrafluoroethylene (PTFE) was blended with PP resin with the aim of improving the foaming behavior of PP. It was found that the PTFE particles were deformed into fine fibers under shear or extensional flows during the extrusion process, which significantly increased the melt strength of PP from 0.005 N to 0.03 N (PP/PTFE with PTFE content of 4.0 wt %) at 230 degrees C. The experimental results indicated that the presence of PTFE improved the cell morphology of PP foams and broadened the foaming window of PP. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013