Energy efficient process and apparatus are disclosed for forming migration free glass fiber packages composed of fibers (16) bearing substantially uniform coatings of size composition. Heated air from around the fiber forming bushing (12) is drawn into a chamber (56) through which the glass fibers (16) pass to cause the water or solvent in the applied size to be evaporated. The flow of heated air through the chamber (56) is regulated so as to obtain substantially uniform size application to the fibers (16).