The thermal conductivity of foams. I. Models for heat conduction

The transfer of heat through a cellular material is considered, taking into account conduction in the solid and gas phases, but excluding radiation and convection. Formulae are derived which relate the apparent conductivity of the material to the conductivities of the component phases and to the density. Some published methods of reaching such a conclusion are critically reviewed and compared. It is shown by binomial expansion that the various formulae tend to the same approximate result for foams of low density.