Facts About Heat Reduction

Heat Gain is measured in BTUs per hour per sq ft of glass falling on a window. It is a function of time as well as temperature.  Window film works because it reduces incoming heat to a rate that allows the air conditioner, fan, or even the breeze to more easily remove the heat and thus make the space more livable.

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 BTUs (heat) coming through the filmed glass compared to the BTUs coming through the plain glass.  The lower the number, the better the heat reduction.  

This is the number architects and 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 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.  Some dealers cite this number as the heat reduction of their film.  Total Solar Energy Rejection is "hype". The true measure of heat reduction is the shading coefficient as explained above.

Heat Reduction is:

SC of Glass - SC of Filmed Glass

SC of Glass

Heat Reduction is not Total Solar Energy Rejected!

Our specifications always compare filmed glass to plain glass.  

All 3M 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 than they do on dual pane glass.  This is because dual pane glass is more efficient to begin with.  Comparing Shading Coefficients before and after film is 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.