Sizing agent for yarns comprises (OH-substd. 1-4C alkyl)-guargalactomannan (10-90 pref. 30-70 wt.%) and (OH-substd. 1-4C alkyl)-cassiagalactomannan (90-10 pref. 70-30 wt.%), dispersed in water to give a 10% aq. soln. (viscosity 20-10,000 mPas at 80C). Opt. starch, its derivs. and/or dextrins may be included.
