UV Plexi and ratings info:
Plexiglass Sheet - UV Filtering
Plexiglass sheet in Ultra Violet formulations reduces damaging UV lightwaves.
NOTES ON ULTRAVIOLET TRANSMITTANCE & Absorption/FilteringGeneral Purpose Plexiglas® sheet absorbs short wavelength ultraviolet (UV) energy, but transmits most of the long wavelength UV (those wavelengths just short of the visible region). The total UV energy absorbed is about 65%.
This unsurpassed UV stability gives General Purpose Plexiglas® MC and G sheet superb weatherability and makes it the logical choice among plastic materials for outdoor and artificial lighting applications. The absence of visible changes in Plexiglas sheet after prolonged outdoor or artificial light exposure means that no change has taken place in the spectrophotometric characteristics of the material in the ultraviolet and visible range. Plexiglas sheet exhibits an increase in UV absorbance caused by sunlight. Most of the drop in UV transmittance of Plexiglas sheet takes place in the first two years. Absolutely no change occurs in the spectrophotometric curves of these exposed samples between 5 and 10 years outdoors. Plexiglas MC acrylic sheet absorbs 65-70% of all UV rays as a standard spec.
Colorless General Purpose Plexiglas sheet exhibits the same excellent resistance to discoloration when exposed for 20 years or more to constantly lit fluorescent lamps, even when the Plexiglas sheet is only two inches from the lamp.
UV Filtering Plexiglas: Some applications, such as document preservation, call for a filter material that blocks more UV energy than ordinary glass but minimal visible light. Cell Cast acrylic Plexiglas G UF-3 and extruded Plexiglas MC UF-5 acrylic sheet absorbs 98% of all UV rays, as well as a small amount of visible light. Plexiglas G UF-4, developed for mercury vapor lighting applications, can also be used as a protective shield. Plexiglas G UF-4 sheet does transmit slightly more UV energy than Plexiglas® G UF-3 and Plexiglas MC UF-5 sheet.
ACRYLITE® UV filtering (OP-3) sheet is pure protection from the irreversible effects of UV damage. It protects from both natural and artificial light. Continuously-manufactured ACRYLITE UV filtering (OP-3) sheet filters out 98 percent of damaging UV rays, protecting paper-borne artwork, prints and documents from fading, yellowing and brittling. ACRYLITE sheet’s UV protection is part of the structure of the sheet, it can’t scratch off!
ACRYLITE® OP-2 sheet guaranteed defect free with a high UV filtering and a crystal clear edge, this cell cast sheet is the clear choice for museum vitrines. Easily fabricated, edges can be mitered and cemented for strong nearly invisible joints. It can be thermoformed, cold-formed, screen printed and painted. This product is also available with an abrasion and chemical resistant coating upon request.
ePlastics stocks UV Filtering plexiglass in 1/8" and 1/4" thickness for protecting fine art and building custom museum vitrines.
Thickness tolerances are plus/minus 10% on acrylic sheet. Thickness can vary throughout the sheet. Normally we see plus/minus 5% or less differences. Use this list as a guide converting fractions to what is actually produced industry-wide.
1/8" = .118" = 3mm
3/16" = .177" = 4.5mm
1/4" = .236" = 6mm
from :
http://www.eplastics.com/Plexiglass_Acrylic_Sheet_UV_Filter