Interior vs Exterior Solar Shade

We have had both exterior sun shades and interior sun shades. My current coach has interior roll down sun shade. It is 'adequate' for the Arizona sun, but not great. Our previous coach had snap on solar shades for the outside front windshield and were superior to keeping out the suns heat. The problem with interior shades is the sun comes in through the windshield and gets trapped in the space between the windshield and the interior solar shade and the heat just builds up and builds up ..... and radiates right through the interior solar shade. Its a matter of physics. The best heat prevention is to block the sun BEFORE it comes through the windshield.