The purpose of this work is to study the radiation heat transfer through some typical ultra‐fine powder insulations. The spectral extinction coefficients for these powders have been measured via infrared transmission measurements. The experimental results are compared with both the dependent and independent scattering and absorption theoretical calculations. The radiative transport process is modeled by the diffusion approximation method. Based on the experimental data, the radiant thermal conductivity between two concentric cylinders and spheres was calculated. The results show that the radiant thermal conductivity between two concentric spheres is about 50 percent higher than that between two cylinders.