The "scattering characterization" that was developed in Marseilles enables us today, with the help of complementary tools (causal model, isotropy degree, ...), to point out the origin of micro-roughness in optical coatings without any ambiguity. Each material can be associated to a key parameter that characterizes its scattering. These parameters can be determined through measurements performed on one single layer, and then can be used to predict scattering in more complex systems. Experimental results (IAD, IP) are presented and show that in most cases, scattering measurement of substrate is sufficient to predict scattering from any coating with a high accuracy. However, at very low scattering levels (under 10-6), this prediction is limited by the presence of local defects in the coatings.