How Low-E Glass Works 

On my Andersen "Sunglass" stuff they use two coatings one of each inside surface, i think, verses the non sunglass windows with only one coating. Sunglass versions are really amazing in stopping the direct hot sun from making rooms uncomfortable, versus just stanard low e stuff, big differences in coatings. cardinal glass is another big maker of this stuff. Windows are so much more than just glass today, science in action..it matters