A great number of empirical or analytical relations can be found in the literature for different properties of porous materials, e.g. permeability, elastic modulus, thermal expansion, as a function of the porosity. These relations are frequently used to estimate the properties of porous materials when direct experimental evaluations are not available. This is a great advantage, particularly in preliminary calculations, when limited information about the materials is available. The porosity dependent relations for material properties are also used in numerical modellings to follow the variations of material properties during a process involving porosity evolution, e.g. a thermo-hydro-mechanical loading or chemical dissolution. It is clear that the use of a given relation in one of the mentioned applications should be compatible with the conditions for which the relation is obtained as different porosity variation mechanisms result in different variations of the material property with the porosity [1, 2]. A good understanding of the variations of the material properties with the porosity will help a proper application of the porosity dependent relations. The aim of this paper is to elucidate the relation between the thermal expansion coefficient of heterogeneous porous materials with their porosity. The presented study concerns the thermal expansion of porous materials with similar solid phases and different porosities, which can be for example the case of porous rocks with similar solid phase or hardened cement pastes with differentwater-to-cementratios.