Abstract: A composite material is described which is characterized by a substrate based on glass fibers, mineral fibers or derived timber products and by a nanocomposite which is in functional contact with said substrate and is obtainable by surface modification of a) colloidal inorganic particles with b) one or more silanes of the general formula (I) Rx—Si—A4-x  (I) where the radicals A are identical or different and are hydroxyl groups or groups which can be removed hydrolytically, except methoxy, the radicals R are identical or different and are groups which cannot be removed hydrolytically and x is 0, 1, 2 or 3, where x≧1 in at least 50 mol % of the silanes; under the conditions of the sol-gel process with a below-stoichiometric amount of water, based on the hydrolysable groups which are present, with formation of a nanocomposite sol, and further hydrolysis and condensation of the nanocomposite sol, if desired, before it is brought into contact with the substrate, followed by curing.