This article presents the mechanical behaviour of rigid polyurethane foams with relative density (ρf/ρs) above 0,3. The parameter taken into account is the density, which controls the foam architecture. The mechanical properties of the foams, characterised by large deformation compression tests and dynamic mechanical analyses, were compared to two theoretical models: (i) the Gibson and Ashby approach, widely used for foam description and (ii) the 2 + 1 phase model from Christensen and Lo, generally used for the description of particulate composite materials. In the studied density range, it is shown that the second approach is more appropriate. Moreover, the stress–strain curve and in particular yield stress have been modelled using two different approaches by extension of this model to the non-linear domain.