Beat the Heat for Cheap: Reflective panels for your windows

Over the past seven summers I've spent working in great part from my fourth-floor walkup, I've learned that it's not the heat; it's the sunshine. On hot but cloudy days, my apartment remains reasonably comfortable because the sun is not heating the building's brickwork facade. But on hot and clear days, my east and south-southeast exposures are killers: not only does my own place get the radiated results of all that sunlight, but so do the three units below me -- and as we all know from high school physics, heat rises.

Happily, since I moved here the roof has been reclad in reflective material, which helps cut the heat input from above, at least. And I've learned that this same principle can apply inside my apartment, too.

On most of my windows I have dual-layer cellular blinds, which strike a decent compromise between insulation and translucency. While they do allow some light (and thus heat) into my space, a good portion of that energy is trapped in the air pockets of the blinds. These are a pretty pricey investment, though. A cheaper option is to simply cover the windows in reflective material, just like the roof. If that sounds complicated, it's not. You, I, and nearly every other person in the city is well stocked with a really fabulous reflective material. It's called aluminum foil.

For years I taped aluminum foil over the bathroom window during summer, to keep that room (and that end of my apartment) as cool as possible. It worked great -- easily lowering the temperature in there by 10 degrees F. or more -- and made sense because:

• The bathroom window is small, so taping it over with foil is an easy task.
• I don't spend a whole lot of time in the bathroom, and thus don't regret the light deprivation.
• The cats, who don't care about the light one way or another, use the cool tile as their refuge from summer heat.

But taping up the foil had disadvantages as well. It looked kind of crappy. I couldn't open the window on pleasant days without taking it down. When I took it down, it tore. Eventually I could not tape up the tears and the foil both, so I had to crumple it up for recycling and use new sheets, which seemed like a waste.

So this year, I've upgraded, by making reflective panels to put in the bathroom window. They look a lot better than sheets of foil held up with duct tape, and work a bit better too. And it's easy to do.

How to make reflective insulating window coverings

Materials:

• 3/16 inch thick foamboard
• Heavy duty cutting blade (Xacto or similar)
• Several yards of aluminum foil
• White school glue (Elmer's or similar)
• Some cellophane or other clear tape

Instructions:

1. Measure the casing of the window you want to cover from edge to edge (width), and top to bottom (height) and write down that measurement in inches. The casing is the "box" or framing around the window frame itself.
2. Multiply the width by the height. This number is the total area, in inches, that you need to cover.
3. Take these measurements with you to an office supply or good crafts supply store. Find some sheets of foambard -- I used 3/16 inch foamboard, which struck a nice balance between sturdiness, insulation, and ease of cutting. Buy enough to cover the total area of your window (you'll likely need to make more than one panel per window).
4. When you get home, figure out the best way to cut the foamboard so that you'll have enough panels to fit your window. For instance, if your window is 30" wide and the foamboard is 36" wide, you'll want to trim it by about 5 3/4", leaving a little bit extra to help jam it into the casing.
5. Cut as many panels as you need to out of the foamboard to cover your window (foamboard usually comes in packs of three sheets or more; I reserve one to use as the cutting mat for the others, so that I don't cut into the floor or table on which everything is laying).
6. Once this is done, rip a sheet of aluminum foil off the roll, one that is long enough to wrap around the entire board with some overlap.
7. Lay the foam board on the foil, and wrap the foil around it more or less like you would wrap a box with giftwrap -- with the highly shiny side facing outwards.
8. I smear some glue on the board and then smooth the foil down over it, to help hold the foil in place, and then tape the edges with the cello tape.
9. Use as many sheets of foil as you need to, to completely cover the board.
10. Once completed, trot that board over to your window and wedge it into the casing.
11. Voila! You have created a super-cheap, heat-reflecting insulated window covering!
12. Repeat until your window is as covered over as you want it to be, times as many windows as you want to cover.

Strictly speaking, you don't need to wrap the entire piece of foamboard in foil, only the side that will be facing out. I did it this way because the result looks a bit nicer on the inside.

If you have a wall thermometer, stick it in the room after you cover the window(s), and check it every once in a while. I can almost guarantee that you'll be amazed at how fast and far the temperature drops.