A unifying equation for five fundamental effective thermal conductivity structural models (Series, Parallel, two forms of Maxwell-Eucken, Effective Medium Theory) was derived. A procedure for modelling complex materials as composites of these five basic structural models using simple combinatory rules based on structure volume fractions was proposed. The combined models have advantages over other generic models such as the semi-empirical Krischer model, in that each has a distinct physical basis, and that they are not dependent on any empirical parameter. As a by-product, a physical description has been identified for Levy's model, which was previously used with reservation by some researchers because it was derived solely by mathematical reasoning without any explicit physical basis. (c) 2006 Elsevier Ltd. All rights reserved.