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The Case of Improving the “U” Value of Glass

Question Regarding Increasing the “U” Value of Glass:

Dear Glass Detective,

We have glazed windows and need to improve the overall U factor from .338 to .35. Is there an aftermarket film that will increase U factors?

-Jim F.

Answer to Question Regarding Increasing the “U” Value of Glass:


Thank you for contacting the Glass Detective with your request regarding the use of window film on glass to improve the overall “U” value of a glazed opening. The quick answer is yes, an aftermarket film can increase “U” value. The bigger question, however, is “how much” improvement will you get. Your question is very specific and you are looking for an improvement of less than 1%. The right film selection could achieve that. I am going to recommend that you contact a reputable window filming company in your area and review what is available that could get you to where you want to go. Good luck with your project.

-Glass Detective

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  • I am a little late to the party, but the basic premise of the original question is wrong.

    If the current windows have a U factor of .338, the performance of those windows won’t be improved by “raising” the the U factor to .35. Unlike R value, U value (or U factor) performance is improved when the number is lower, not higher.

    If the original window performance is U.338 and there is a minimum requirement of U.35, then nothing need be done, the windows have already surpassed the U.35 requirement.

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