In the present work, an investigation was made for the heat transport through insulation powder evacuated under high vacuum. Experiments for heat flux in the powder were carried out from the room temperature down to liquefied helium temperature, which enables us to examine the relation between the heat flux and absolute temperature. Furthermore, the general solution of Wang and Tien for total heat transfer for combined radiation and conduction problem was applied to the powder, was compared with the experimental result. We then quantitatively determined the roles of the contribution from both radiation and conduction, the effect of added aluminium powder and extinction coefficient for radiation in the basic heat transfer mechanisms of the powder in the low temperatures.