disclosed are a process for the preparation of synthetic filaments or fibers and a composition for use as an auxiliary agent in the production of such fibers and filaments . the composition comprises a butylene oxide adduct of a fatty alcohol oxyethylate having the formula r -- o --. sub . n --. sub . m h wherein r = c 8 - c 26 , n = 1 - 20 , and m = 1 - 5 and preferably at least one additional chemical treating agent for the synthetic fibers and filaments . the process includes the step of applying this composition to a fiber or filament .