Window Film Basics: Heat Reduction

How do you know the heat reduction of a film?

The Shading Coefficient (SC) of a film is the number that expresses the heat reduction of that film. In the window film industry, it is defined as the ratio of BTU's (heat) coming through the filmed glass as compared to the BTU's coming through the glass without film. The lower the number, the better the heat reduction.

This is the number that architects & engineers use in heat load calculations, and it is how we represent the heat reduction of our films.

Total Solar Energy Rejected is a quantity used by many window film dealers to express the heat reduction of their film. It is a measure of the energy reduced over the entire solar spectrum, not just the heat portion. It is inflated and inaccurate and we never use it. The true measure of heat reduction is the Shading Coefficient, as explained above.

Our specifications always compare filmed glass to plain glass

All 3M window film sample cards display information for 4 types of glass (an example is shown to the right). This gives you realistic expectations for our products. The same piece of film on different types of glass will yield different results.

Films make a bigger improvement on single pane glass as compared to insulated (or dual pane) glass. This is because insulated glass is more efficient to begin with. Comparing Shading Coefficients before & after film has been applied shows that the change in performance is not the same.

Sample cards from other film manufacturers give data only for clear single pane glass and their dealers would have you believe that their film yields identical results on all glass. This is absolutely incorrect!

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