Abstract: This invention is directed to a method for treating fibers by applying thereto a compound having the general formula ##STR1## wherein R.sub.1 is alkyl from 1 to 23 carbon atoms, R.sub.2 is alkyl from 1 to 23 carbon atoms, n is a number from 3 to 15, and X is --C.sub.2 H.sub.4 O-- or --C.sub.3 H.sub.6 O--, or a mixture of --C.sub.2 H.sub.4 O-- and --C.sub.3 H.sub.6 O--.