uPVC, or unplasticized polyvinyl chloride, is a strong and rigid vinyl made without plasticizers. Unlike PVC, common to plumbing and pipes, uPVC does not flex, is durable and functions well in a wide range of temperatures and operating pressures. Incredibly stiff, uPVC can stand up to outdoor environments and a variety of chemicals without corrosion, pitting or oxidation. Because of these qualities, uPVC is ideal for window frames and sashes.