Abstract: Polyester yarn having portions which differ in dye uptake, arranged along its length in a predetermined pattern, is produced by treating portions of a spin-oriented yarn with a fluid to induce crystallization and then drawing the yarn to provide a product having a break elongation appropriate for the intended use. The spin-oriented yarn is preferably prepared by melt-spinning polyethylene terephthalate into yarn while withdrawing the yarn from the spinneret at a take-off speed of 3000 to 4000 yards per minute. Suitable treating fluids include acetone or methylene chloride at room temperature and water or air at elevated temperatures. The treated yarn can be draw-textured on false-twist texturing machines having heaters at temperatures above 200.degree. C. The treated portions of the yarn dye deeper than the untreated portions to provide attractive effects in dyed fabrics.

Abstract: Yarn of polyester filaments having a random distribution along the filament length of thick and thin sections, which differ in dye uptake, is produced by incompletely drawing a spin-oriented yarn, preferably one prepared by melt-spinning polyethylene terephthalate into yarn while withdrawing the yarn from the spinneret at a take-off speed of 3000 to 4000 yards per minute. The spin-oriented yarn is drawn on a hot draw pin of about 1.3 to 6 cm in diameter, using a draw ratio which is 82 to 95 percent of the draw ratio needed to fully draw the yarn. The incompletely drawn yarn can be false-twist textured under conditions conventionally used for fully drawn polyester yarn. The textured yarn provides attractive dyed fabrics due to darker shades of color in the thick filament sections.