Pressure gradient in the insulation materials along the thickness direction, which results from the changes
in pressure around the maneuvering hypersonic vehicles, will lead to gas diffusion and permeation in thermal insulation
materials and affect the insulating property. In order to study the influences of gas diffusion and permeation on materials
insulating properties, a heat transfer model combined conduction radiation with gas diffusion and permeation was
established under Rosseland approximation for radiation heat transfer. The established control equations were solved by
finite volume method and the transient insulting properties under the condition of gas diffusion and permeation were numerically
studied. Results show that gas permeation begins to influence the heat transfer process and worsen transient insulating
property for a 2 cm nanometer insulation material when its permeability is greater than 10-14 m2 under the condition
where the heated surface is at environment pressure of 0.1 MPa and the unheated surface is in vacuum. Gas viscosity
has a significant influence on gas diffusion and permeation process and the diffusion process enhances with the decrease
in viscosity. Extinction coefficient has more significant influence on the thermal response at the insulated surface
than gas diffusion parameters and the temperature response decreases with the increase of extinction coefficient.