In thinking about energy loss and having used Insulpink in my basement, makes me think that homes should be built with insulating shutters. Especially where there are large glass panes like patio sliders. If bifold "doors" or shutters that were insulated, even with r10 rigid foam insualtion that could be shut at night in cold weather, that would really cut down on a pretty nasty heat loss. I've seen something like this advertised, but they're VERY expensive. Economy is expensive! I'm sort of thinking of building something like this and include decorative or at least finished sort of surface that I could press into place on cold evenings. Maybe laminate the inside with a reflective surface, and put a lite board like Luan on the outside and paint it to match the house. Would store it in summer. A minor hassle maybe but a huge gain in reducing heat loss.