Ultrex® (made by Burlington Industries, Inc.) is a waterproof, windproof, durable and extremely breathable fabric system. A microporous coating is applied to the underside of the fabric. The coating produces either a white or gray backing. It is small enough to block out wind and rain, yet large enough to permit perspiration vapor molecules to escape. A durable finish causes water to bead up on the outside to keep the fabric dry. Ultrex® can be applied to any fabric, but is usually applied to Supplex®. This product has been shown to withstand numerous washings before losing it's waterproof abilities.