[en] The effect of porosity on the thermal diffusivity and elastic modulus has been studied on artificially aged, free-standing thermal barrier coatings (TBCs) produced by air plasma spray (APS). The activation energy of the sintering phenomenon was estimated from the variation in diffusivity with time and temperature. X-ray diffraction was used to evaluate the phase stability of 7 wt.% yttria partially stabilized zirconia (YPSZ) coatings. The thermal diffusivity and elastic modulus as measured by photothermal techniques and three-point bending, respectively, are reported as a function of the ageing time. Correlations between the thermal and mechanical parameters are investigated by suitable models based on the microstructural features revealed by electron microscopy. The reliability of porosity information provided by image analysis and used as input for the modelling is critically discussed