The analysis of the X-ray diffraction patterns scattered at small-angles (SAXS) by porous materials is a powerful analytical tool providing relevant structural information on supported metals used as heterogeneous catalysts. In particular, the technique offers valuable structural insights on the interphases which govern the chemical behaviour of these materials. Using a series of silica-supported palladium catalysts we show how SAXS experiments address the crucial importance of porosity (or “nothing”) in affecting the structure of these catalysts.