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English: Heat transfer mechanisms within micro porous thermal insulations.

"Within a porous insulation material, heat is transported through three different mechanisms: conduction heat transfer through the solid backbone, thermal conduction within the gas phase, radiative heat transfer and can be approximated by the sum of the thermal conductivity of the solid, λs, the thermal conductivity of the gas within a given porous structure, λg, and the radiative thermal conductivity, λr."

"The thermal conductivity of typical microporous insulation materials such as glass fibers and large-pored foams is shown:

The saturation region where diffusive heat transfer occurs can be clearly observed. In this case, the thermal conductivity is almost independent of the gas. The thermal conductivity of the pore gas microporous materials is already reduced and a total effective thermal conductivity below or in the range of the thermal conductivity of still air can be observed. The thermal conductivity values indicate the sum of the thermal conductivity of the solid and the radiation coefficient, λs + λr."

"Heat transfer occurs by heat conduction through the solid 'skeleton,' the gas phase and by heat radiation."

This scheme provides insight until realization of superinsulators:

"The reduction of pore size to less than 1 μm would result in thermal insulation products having thermal conductivity lower than that of still air."

"The ability to evacuate porous insulations would lead to effective thermal insulation systems with thermal conductivity values about 10 times lower than known conventional insulation materials."

Author Hans-Peter Ebert cited from the source on 2024-02-19: https://www.researchgate.net/publication/282389684_Functional_materials_for_energy-efficient_buildings

Ebert, H.-P. (2015) 'Functional materials for energy-efficient buildings'. EDP Sciences - SIF. p. 2 and 3