Best way to keep the sun's heat from the front away ?

Hi,

Actually most windshield glass is a triple layer of glass/plastic/glass. (i.e. "safety glass") It's one reason it costs lots.

If you wish to believe that a sun shield inside works better than a similar covering on the outside, please point me to an experiment that shows that result.

May I point out the OP asked "the best way". Not the cheapest or most convenient way?