TiO2/MgF2 bi-layers were prepared by sol-gel processing in both stacking sequences. Films were characterized by scanning electron microscopy. UV-vis spectrometry, and ellipsometric porosimetry. The results obtained by the different methods are compared. The validity and limitations of the respective techniques are discussed with special focus on film porosity and the interface between the TiO2 and MgF2 material. (C) 2011 Elsevier B.V. All rights reserved.