I did an experiment today to see how much the 3M Crystalline (CR70) tinting helps to reduce cabin heating when parked in the sun. The answer is "basically nothing" or at best of 1 degrees lower temperature after 30 minutes (116 degrees vs 117 degrees). Here are the details:
The Blue Model 3 has 3M CR70 on the sides and back window (the front cannot be done without risking blowing up the computer as discussed in other threads). The Black Model 3 has no tint. So question: is it worth it to get the 3M tint?
I cooled the cabins on both to 74 degrees. I then pulled them out into the courtyard in front of our garage where they could be exposed to the sun side-by-side with no shade. Then I watched and waited (I recorded the app as it tracked the temperature changes, so I may get around to editing a video of the experiment but it is a huge file so ...) To be sure, I repeated the experiment twice.
The two vehicles increased in temperature more or less in lock step both times. By the end of 30 minutes the Black M3 (no tint) was at 117 degrees and the Blue one (with tint) was at 116 degrees. (One could argue that since the black car absorbs more heat than the blue one, the deck was stacked in favor of the 3M tint.)
So the question is why? We know the tint rejects 97% or infrared and 50% of total solar (or at least that is what the manufacturer says), so what gives? It is probably the windshield and maybe (though I doubt it) the pano roof. Since the windshield is un-tinted because of that computer issue, there is still plenty of greenhouse effect there and even if we are rejecting heat from the side and back, it is not enough to make a difference.
In any case, proof positive that the 3M crystalline tint is a total waste of money to put on the sides and on the back if your intention is to a) keep the vehicle cooler while parked or b) help the AC work less when driving.