"You can find retailers of UV filtering Lexan/Plexi-glass on the web. =
Acrilyte is one trade marked brand that can feature UV resistance. The =
thing to remember is that not all Lexan is UV resistant-you have to =
specify."

It is my understanding that all "Lexan" does filter out 90%+ of the UV. Lexan is a brand name for polycarbonate plastic sheet. Polycarbonate absorbs UV. It is true that acrylic sheeting like Plexiglass does not filter UV unless UV absorbing materials are added to the acrylic resin. UF-2 and UF-3 Plexiglass are other brands of acrylic sheeting that filter UV. It would be true to say that "not all plastic sheeting is UV resistant." While filtering out the UV is essential, excessive visible light levels can also cause fading and deterioration, especially of textiles and watercolors or tinted prints. Therefore, I also recommend that if one is going to the expense and trouble to install plastic sheeting over windows, they should purchase tinted sheeting to reduce the total amount of light entering the building. 50% tinting can hardly be noticed, and even 80% tinting still allows the windows to be "read" as windows while significantly reducing the amount of UV and visible light entering the room. However, once 80% tinting is used, it is necessary to use artificial lights to illuminate the room interiors. We like the bronze tinting better than the gray tinting as it imparts a warm "glow" to the room rather than a cold tone. Also, it is necessary to cover all the windows in the room with the sheeting with the same degree of tinting, or some windows will be lighter than others. 

Tinted UV filtering Plexi or Lexan must be special ordered and your local supplier will probably have to buy several sheets to have the company run the special order. Our local supplier has found that it is good to keep some UF-3 tinted Plexi on hand, as there is an occasional demand for it from Historical Societies, etc. It is also a good idea to install pull-down blinds to block all light when the building is completely closed to the public even if you have UV filtering and tinted plexi sheeting installed on the windows.




Richard L. Kerschner
Director of Preservation and Conservation
Shelburne Museum
PO Box 10, Route 7
Shelburne, VT  05482
(802) 985-3348 Ext 3361

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