Plastic lenses are typically made from acrylic, polycarbonate, CR-39 or polyurethane. Optical discs are made of polycarbonate plastic and aluminum. These are manufactured from polycarbonate or acrylic plastic. Plastic (polycarbonate) sunglasses generally absorb UV radiation. Some of these include carbon composites, plastic material, such as polycarbonate, and aluminum alloys. Polarizers are routinely used to detect stress in plastics such as polystyrene and polycarbonate. Motorbike windshields are often made of high-impact polycarbonate or acrylic plastic. Photochromic lenses may be made of glass, polycarbonate, or another plastic. Some plastic lens materials, such as polycarbonate, inherently block most UV. Therefore, a hard coating is applied to polycarbonate eyewear lenses and polycarbonate exterior automotive components. ASA is compatible with some other plastics, namely polyvinyl chloride and polycarbonate. Subtle blurring is also induced by the poor refractive properties of plastic and polycarbonate lenses. Bisphenol A is a precursor to polycarbonate plastics. Today they are made of modern plastics, like Polycarbonate or fire resistant ABS. Weight was further minimised through the use of a polycarbonate plastic windshield and windows.