Useful hydrophobic materials include for example the above-recited silanes.
Good hydrophobicization is obtained not just with strongly hydrophobic compounds such as for example triethoxy (3,3,4,4,5,5,6,6,7,7,8,8-tridecafluorooctyl) silane; instead, a treatment with methyltriethoxysilane or i-butyltriethoxysilane is completely sufficient to obtain the desired effect.