Remember the company we are talking about is 3M. One major major chemical reaction of sunlight is photosynthesis, others are oxidation etc.
Films for double pains do not create heat and some do not reflect. The chemistry of these films I'm sure is patented so look it up. I do know that it has something to do with them producing a red color when water hits them. You can wet the film I have and it looks pink, wet the darkest tint film and it turns red. The older 3M films were thick, the crystalline is not.
Other companies produce clear films but just not as good so I imagine the patent or the technology is searchable.
This is the best source I found on the chemistry:
http://www.detailingdynamics.com/page/window_tinting
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