In the paper the influence of colloidal silica addition with different amounts of organic resin in facade paints formulations on the change of water vapour permeability of hardened coatings was researched. The results were obtained by means of experiments. To quantify the ability of paint to diffuse water vapour, Sdfactor, defined as equivalent to the thickness of non-rotating air layer, was used. For the quantitative determination of the relationship between water vapour permeability and the share of analyzed components in the formulation of paint a statistical model based on multiple regression was applied. Statistical analysis of the results showed that the effect of changes in the amount of colloidal silica in the formulation of paint on Sd value is small, compared to organic resin share changes.