Ceramic thermal insulator is one of the important thermal management devices for SOFC operating at medium temperatures (<800 degrees C). This study used colloidal dispersion, direct foaming method, microwave drying, and sintering to prepare porous Al2O3 foams with total porosity of 85-95%. The measurement of thermal conductivity by a hot-wire method was conducted. The effects of cell structure on thermal conductivity were investigated with scanning electron microscopy (SEM) and Fourier transformed infrared spectroscopy (FTIR). By optimizing the cell structures of Al2O3 foams, low thermal conductivities of 0.05 W m(-1) K-1 at room temperature and 0.14 W m(-1) K-1 at 800 degrees C were achieved in this study. (C) 2011 Elsevier B.V. All rights reserved.