Well, when it's -5 degrees outside, leaving them down is a bit uncomfortable.

 

3-M makes a new tint that blocks out 97% of the heat rays even when you choose the lightest tint...clear. You could tint your windshield, tint is impossible to see and you don't have the heat. Imagine doing your entire car, med tint and clear on the windshield and never have your interior fade or crack, and always be cool.
Gary