I stumbled upon your site after going to the government energy site. I have a large sliding glass door in my condo that I need to block somehow in the summer so that the heat doesn’t come through, the condo gets unbearable. Should I get the reflective aluminum foil and tape it up on the windows? Hope you can send some advice.
What we’ve found most effective and convenient is to use a reflective insulation — one like a number of members sell that has 2 reflective surfaces with a core of double bubble polyethylene film. Some of the hardware and box stores carry one of the brands and they all are pretty much alike. Just cut the material to size and attach to the door frame — Velcro works fine for this and you can remove and reinstall easily. Other products will work well, however, people have found the structure I recommend is easier to work with than thinner ones like radiant barriers. The good news is that this will completely block the effects of the sun on the door. The bad news is that it will completely block the light. You might want to make some modifications like cutting a small opening so that you can see out, or installing in such a way that you can fold an opening part of the way. Using the Velcro system makes removal pretty easy.