The thermal conductivity of ceramic powder packed beds was measured at temperatures below 100degreesC for various powder sizes and compositions and under different gas atmospheres. Measurements at low pressures (down to 10Pa) combined with a theoretical model allowed the elucidation of geometrical and thermal resistance parameters for the contact points between granules. The gap thickness and contact point size were found to be well correlated with the mean particle size. The thermal conductivities of all powders at low pressure were found to differ at most by a factor of two, whereas the solid-phase conductivities of the powder materials differed by more than one order of magnitude. A theoretical model accounting for the sizedependence of contact point conductivity is incorporated to rationalize this trend.