Abstract: Water-insoluble condensation products, obtained by the condensation of a mixture containing as essential components(A) from 80 to 99.9 mol %, based on the sum of (A), (B) and (C), of a mixture consisting essentially of(a) from 30 to 99 mol % of melamine and(b) from 1 to 70 mol % of a substituted melamine of the formula I ##STR1## where X, X' and X" are each selected from the group consisting of --NH.sub.2, --NHR and --NRR', and X, X' and X" are not all --NH.sub.2 at one and the same time, and R and R' are each selected from the group consisting of hydroxy-C.sub.2 -C.sub.10 -alkyl, hydroxy-C.sub.2 -C.sub.4 -alkyl-(oxa-C.sub.2 -C.sub.4 -alkyl).sub.n, where n is from 1 to 5, and amino-C.sub.2 -C.sub.12 -alkyl, or mixtures of melamines I,(B) from 0.