Microcellular injection molding offers many advantages such as material and energy savings, reduced cycle times, and excellent dimensional stability. However, typical surface characteristics of microcellular injection molded parts-such as gas flow and swirl marks and a lack of smoothness-have precluded the process from being used for applications where surface appearance is important. This article presents an insulator-assisted method that has been shown to improve the surface quality of microcellular injection molded parts significantly. By incorporating a thin film (75-225 mu m) of polytetrafluoroethylene (PTFE) insulator on the mold surface, the polymer melt-insulator interfacial temperature can be manipulated and can be kept high enough during mold filling to reduce or eliminate swirl marks on the surface. The experimental results in terms of surface roughness and surface profile of conventional and microcellular injection molded parts with and without the insulator film are discussed. Thermal analyses of the corresponding microcellular injection molding experiments were performed to elucidate the correlation between film thickness, interfacial temperature, and the surface quality. The effect of insulator on the cooling time increase is also analyzed and presented. POLYM. ENG. SCI., 50:1281-1289, 2010. (C) 2010 Society of Plastics Engineers