Abstract The present analysis proposes an extremely simple, yet very effective, alternative for the determination of effective thermal conductivity (ETC) of open-cell foam-like structures for any working fluid (characterized by the kf/ks ratio) based on the predicted ETC under vacuum condition. In order to arrive at the final recommendation, detailed numerical investigation is carried out by considering two generic cellular porous structures, as well as four real foams. The study clearly demonstrates that the ETC of porous medium under vacuum condition (i.e., when kf/ks→0) contains the necessary quantitative structural information as far as the thermal conductivity is concerned. Therefore, the ETC of the same porous medium for any working fluid can be evaluated from an appropriate simplified model and the only parameter used in the model can be directly calculated from the ETC under vacuum condition. From the results obtained during the present study, four different models are proposed for the ETC, covering the entire range of kf/ks ratios lower than unity. The proposed method, along with the predictive models, provide accurate estimations for the ETC of open-cell foam-like structures and can also be used for the indirect measurement of the ETC in presence of hazardous working fluids.