The present invention relates to a process for preparing a surface treated filler material product with succinic anhydride(s), a surface treated filler material product, a polymer composition, a fiber and/or filament and/or film and/or thread comprising the surface treated filler material product and/or the polymer composition, an article comprising the surface treated filler material product and/or the polymer composition and/or the fiber and/or filament and/or film and/or thread as well as the use of a mono-substituted succinic anhydride for decreasing the hydrophilicity of a calcium carbonate-containing filler material surface and the use of a surface-treated filler material product for initiating the crosslinking reaction in epoxide resins.