We created a blend between a TiO 2 sponge with bimodal porosity and a Methyl-Ammonium Lead Iodide (MAPbI 3) perovskite. The interpenetration of the two materials is effective thanks to the peculiar sponge structure. During the early stages of the growth of the TiO 2 sponge, the formation of 5–10 nm-large TiO 2 auto-seeds is observed which set the micro-porosity (< 5 nm) of the layer, maintained during further growth. In a second stage, the auto-seeds aggregate into hundreds-of-nm-large meso-structures by their mutual shadowing of the grazing Ti flux for local oxidation. This process generates meso-pores (10–100 nm) treading across the growing layer, as accessed by tomographic synchrotron radiation coherent X-ray imaging and environmental ellipsometric porosimetry. The distributions of pore size are extracted before (> 47% V) and after MAPbI 3 loading, and after blend ageing, unfolding a starting pore filling above 80% in volume. The degradation of the perovskite in the blend follows a standard path towards PbI 2 accompanied by the concomitant release of volatile species, with an activation energy of 0.87 eV under humid air. The use of dry nitrogen as environmental condition has a positive impact in increasing this energy by~ 0.1 eV that extends the half-life of the material to 7 months under continuous operation at 60 C. View Full-Text