Here is a reply I got from the overlay Manufacturer:
PETG UV protection for poster graphics
PET/PETg is Polyethylene Terephthalate, its polymer type is thermoplastic. The processing is to modifiy the very dry PET granules with high moulding temperature.
Exposure to sunlight and some artificial lights can have adverse effects on the useful life of plastic products. UV radiation can break down the chemical bonds in a polymer. This process is called photodegradation and ultimately causes cracking, chalking, color changes and the loss of physical properties. To counteract the damaging effect of UV light, UV stabilizers are used to solve the degradation problems associated with exposure to sunlight. When stabilized with UV stabilizer, it has the least discoloration. UV stabilizer maintains the clear appearance of PET and PETG sheet during long-term weathering. The UV Absorbers improve the color stability and tensile properties when exposed to sunlight.
We can clearly say while UV Absorbers improve the color stability and tensile properties when exposed to sunlight and the PET/PETg protects the graphic/poster placed underneath from approx. 97% of UV damage.
But because this is a thin plastic product, it will not have the UV protective levels of a top line “Museum glass” Tru Vue” product:
http://www.tru-vue.com/products/museum-glass-anti-reflective This is the ultimate in UV protection, but is very expensive and is available in glass only. For example, a 24” x 36” Tru Vue museum glass costs $100 to $150 each.
UV protection is never 100%, so one must try to mount frames where direct sunlight will not hit -if there is a choice to mount away from direct sunlight. Make sure that it is clear that people don’t expect 100% protection for UV, more like 97%. The 3% means that some fading can still occur depending on the duration of exposure to UV (how many hours a day is poster exposed to sunlight and whether directly/indirectly). So, the rule of thumb is to mount posters away from sunlight or other bright light constantly hitting the image to minimize or eliminate the impact of UV using this UV protected PETG.
If a client is wanting to protect from UV damage to a high value poster, than we’d suggest either making sure it mounted away from any bright lighting, either sun or bulb lighting. Or, mounting the poster conventionally and using museum grade UV protective glass. The darker the mounting environment, the better protected against UV damage. That’s why museums always have subdued/low lighting.
Please use the above information to evaluate the best mounting location to avoid potential UV damage to graphics/poster.
