Originally Posted by
cyccommute
Depends on the type of plastic, whether coating is applied to it and the wavelength of the radiation. 300 to 400 nm wavelengths go through plastic easily. UVB is from 280 to 320 nm so part of it could pass through many plastics. Altitude also has an effect also since the UV flux increases about 10% every 3000 feet.
Polycarbonate, which is what safety goggles are usually made of, is essentially opaque to anything shorter than 380 nm. Other plastics used have similar cutoffs, with the except of CR39 and other ADC plastics, which are have cutoffs at about 350 nm, without a coating, but even that blocks 90% of UVA. (CR39 is the most common plastic used in eyeglasses, having pretty much the same optical distortions as glass, but lighter (and cheaper, and easier to work with, and tougher, and resistant to lots of solvents, and to heat.) It also takes tints very well, so is used in sunglasses, but I don't know how widely).
Optical glasses are another matter, and need coatings to be UV opaque.