The U.K. is in the midst of an absolutely brutal heatwave right now, with record-breaking temperatures (opens in new tab) across the country. Some parts have expected temperatures as high as 109 degrees Fahrenheit (43 degrees Celsius).
Unlike places that regularly deal with such temperatures, British homes are not built for extreme heat. They’re all about keeping heat in, and once it’s there it’s going nowhere. Fortunately I found a way to keep the heat out, with a little help from some aluminium foil.
Over the weekend social media (opens in new tab) was filled to the brim with tips on how to stay cool, and keep the inside of our houses as cool as possible. Those tips included things like keeping windows shut to keep hot air out, drawing the curtains to reflect sunlight and, you guessed it, covering the windows with aluminum foil (opens in new tab).
Foil is shiny, and shiny things reflect sunlight — the main source of heat at the moment. Since the front of my house is south-facing, it gets a lot of sunlight, and since there are no buildings to provide some cover the sun is shining on it almost as soon as it rises over the horizon.
For that reason, my bedroom has been known to hit 80 degrees by the time I wake up on a particularly warm morning. Cue my house looking like it’s cosplaying as the home of an anti-5G lunatic.
It got some weird looks from passers-by, I’ll tell you. It’s not every day you see someone duct-taping foil to their house. But the judgement from strangers is nothing compared to the sweet feeling of a house that is roughly 20 degrees cooler than the outside world.
While my area managed to reach temperatures as high as 98 degrees, the rooms downstairs have stayed below 77 degrees. Upstairs has fluctuated a bit more, especially on day two of the heatwave. Last night was around 10 or 11 degrees warmer than normal, and that meant the house wasn’t able to cool down very much — even with the windows open.
How does aluminum foil keep the heat out?
It does sound crazy that a few dollars worth of aluminum foil can help keep the heat out of your house. Putting any sort of reflective material between a heat source and a target will reduce the transfer of radiant heat. The same principle is used for everything from survival blankets to spacecraft.
However if you have newer windows, the foil won’t make as much of an impact. According to Dr. Rick Sachleben, retired chemist and member of the American Chemical Society, it’s because modern windows also include special coatings that block infra-red light while letting visible light through.
That minimizes the amount of heat coming in during summer, and how much you use in the winter months. Sachleben says foil may help, but not quite as much as it would with older single-pane glass that doesn’t have that coating.
But in either case there are more specialized reflective films such as the Arthome One Way Window Film ($28.98, Amazon (opens in new tab)) that are specifically designed to reflect heat without blocking all visible light, so the window can still be a window. Then again, aluminum foil is a lot cheaper if you only need it for a couple of days each year — especially if you buy in bulk.
What are the downsides to using aluminum foil?
Some corners of the internet have reported aluminum foil left a residue or burn in on their glass. The difficulty of removing the leftovers varies from situation to situation. In some cases, products like Goo Gone and vinegar removed the marks no problem, while others resorted to more extreme measures — including using a glass scraper.
That is definitely worth bearing in mind before you start applying foil to your windows. At the very least it suggests that you should replace it often, and keep a watch out for any potential problems. For what it’s worth, my own windows are looking stain free for the time being. But I taped the foil to the UPVC window frame rather than the glass itself.
The most obvious downside to covering your windows in foil is that it makes you look a little bit crazy. Especially if nobody else is doing it. And, since the foil blocks out all light, you end up spending your day in a very dark house.
That’s the trade-off from blocking out some of the solar heat, and is one of the more noticeable advantages of more specialized options. Those options are also likely to be more durable than super thin sheets of foil. The foil on my own windows is already starting to develop tiny holes, and it’s only been up for 36 hours.
One topic of discussion on British social media was where the foil should be applied. The concern was that placing it on the inside of the windows may cause heat to get trapped between the foil and the glass — heating up the glass and causing it to crack. So the advice being shared was to cover the outside of the window — which is no easy task when you don’t have a very big ladder.
However Dr. Sachleben doesn’t feel this is likely, and that light would simply be reflected through the window the same way it came in. While there may be some buildup between the foil and the glass, he said he’d be surprised if this would cause the glass to break. He also pointed out that specialized window film is typically designed to be installed on the inside. That’s not to say it definitely won’t happen, just that it doesn’t seem that likely.
Bottom Line: Should you cover your windows in foil?
For me, the fact that this sort of extreme heat only happens for a few days each year (for now) means aluminum foil is the perfect option. It's cheap, readily available, and it can be applied and removed very easily. The hardest thing is making sure I have enough silver duct tape, because it feels like using anything else would defeat the purpose.
It certainly seems to have helped keep the inside of my house cool — with varying levels of success. Upstairs is still warmer than I'd like, but thanks to the laws of convection and the there's more direct sunlight means that was always going to happen.
I would prefer to be a lot cooler, there's doubt about it, but for now I'm just happy that I don't have to sit in a pool of my own sweat — or buy one of the best smart air conditioners.
Looking for other ways to beat the heat? Check out our 7 tips for staying cool in a heat wave. Plus, here are 10 tips to cool down a room, 7 tips on how to cool down your car, how to make sure your phone doesn't overheat and the best cooling mattress for hot sleepers.