all unreacted materials the treated wool is then dried in the usual way by treating wool with an acid anhydride and an isocyanate as herein described the wool is chemically modified because there is a chemical reaction between the above reactants and the protein molecules of the wool fibers although the properties of the modified wool indicate beyond question that actual chemical combination between the wool and the reactants has taken place it is not known for certain how the wool and these reactants are joined it is believed however that the reagents react with some of the sites on the wool molecule where there are reactive hydrogen atoms e g amino guanidino hydroxyl and phenolic groups a possible explanation for the effectiveness of the combined treatment is that acylation of the wool by the acid anhydride forms carboxyl groups that swell the wool structure and provide additional sites of reaction for the isocyanate this effect cannot operate when wool is treated with either agent alone it may be however that other reactions occur and it is not intended to limit the invention to any theoretical basis when the reaction is carried out with a diisocyanate for example tolylene 2 4 diisocyanate combination with the wool may establish cross links between protein molecules that may increase the resistance of the wool to attack by chemicals carpet beetles.