The effects of adding polyethylene (PE) in polystyrene (PS) foaming material on the cell structure and the heat transfer of vacuum insulation panels (VIPs) are examined in this study. Several parameters are proposed to describe the foam structure, namely, the broken cell ratio, the average cell size and the solid volume fraction. Adding 2% PE was effective in altering the cell structure and reducing the heat transfer, while adding 5% PE did not improve the performance further. The lowest thermal conductivity found in this study is 4.4 mW m(-1) K-1, which is among the best published performances of VIP. (C) 2009 Elsevier Ltd. All rights reserved.