The total thermal conductivity lambda of resorcinol-formaldehyde aerogel monoliths has been measured as a function of density rho in the range from rho = 80 to 300 kilograms per cubic meter. A record-low conductivity value in air at 300 K of lambda approximately 0.012 watt per meter per kelvin was found for rho approximately 157 kilograms per cubic meter. Caloric measurements under variation of gas pressure as well as spectral infrared transmission measurements allowed the determination of solid conductivity, gaseous conductivity, and radiative conductivity as a function of density. The development of such low conductivity materials is of great interest with respect to the substitution of environmentally harmful insulating foams made from chlorofluorocarbons.

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The thermal and electrical conductivity of monolithic carbon aerogels was investigated at room temperature. Results showed both the solid thermal conductivity and the electrical conductivity scale with the density in the range between 60 and 650 kg m−3. The scaling exponents for the two conductivities have identical values of 1.5. For a density of 82 kg m−3 a thermal conductivity of 0.029 W m−1 K−1 in air and 0.018 W m−1 K−1 after evacuation was found.

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