Men's Nike Flex Training Short - VENTILATED COMFORT FOR EVERYDAY TRAINING. The standard fit of the Men's Nike Flex Training Short features a durable, water-repellent finish to help keep you dry. Combined with a perforated design, you ll be able to stay cool while your workout heats up. Nike Flex fabric stretches with your body for optimal range of motion. DWR (durable, water-repellent) finish helps shield you from the elements. Allover perforations for ventilation and comfort.