Polyvinyl alcohol has been evaluated as a warp size for cotton, Dacron 4 polyester staple yarn, and blends of Dacron staple with cotton and viscose rayon. Under simu lated weaving conditions, superior sizing performance on all these yarns was given by completely hydrolyzed, high viscosity product. This type of polyvinyl alcohol also proved to be effective as an extender for various sizes based on starch or modified starch. The size formulations tested are described.