The effective : thermal conductivity for several loose particulate insulation systems has been measured in the temperature range from 273 K-900 K and the results compared to those predicted from three different models. The measured thermal conductivities increase with temperature. This is accounted for in terms of increased conduction by the fluid (air) and the radiative heat transfer through the media although the latter mode of heat transfer is relatively suppressed in materials containing finer particles. The model due to Zumbrunnen ef al. [1] was found to predict values that closely agreed with the experimental values.