Abstract: A process is provided in which a continuous filament polyethylene terephthalate yarn having an HRV in the range of 24 to 28 is heated to a temperature in the range of 75.degree. to 250.degree. C. and drawn to a total denier in the range of 50 to 500 at a draw ratio in the range of 5.2:1 to 6:1, passed over a draw roll having a temperature in the range of 225.degree. to 250.degree. C., relaxed at a tension in the range of 0.09 to 0.15 gram per denier and wound up at a minimum speed of 2,000 yards per minute (1829 meters/minute). The yarns prepared by this process have a tenacity in the range of 7.5 to 9 grams per denier, a load-bearing capacity in the range of 3 to 5 grams per denier at 7% elongation, a maximum dry heat shrinkage of 4% at 177.degree. C. and an elongation at break in the range of 12 to 20%.

Abstract: Polyester monofilaments of 1000 to 10,000 denier per filament can be produced to have both good straight tenacity and good transverse properties (high loop tenacity) by extruding molten polyethylene terephthalate of at least 0.6 intrinsic viscosity through an air gap into a water bath to form a monofil and then drawing the monofil in two stages under controlled heating conditions to provide at least 0.190 average birefringence, measured along monofil diameters and a substantially lower birefringence value adjacent to the surface of the monofil. The monofilaments are suitable for use as reinforcement in tires, V-belts and other industrial applications.