Yoghurt On Your Windows: Ingenious Solution or Old Wives Tale?
- Home Energy Advice Team
- 1 day ago
- 5 min read
It’s another red heat warning, and with temperatures exceeding 30°C more frequently these days, the question on everyone’s lips is how we stay healthy and happy in the scorching heat.
With the state of the internet these days, it’s hard to know who’s giving you genuine advice on staying cool, and who’s laughing at your expense with an ‘old wives’ tale. We all like a cool breeze -but will you die if you sleep next to a fan? South Korea thinks so! Splashing cold water on your head is refreshing - but will you get the sniffles if you go outside with wet hair?
One of these ‘urban legends’ that our Home Energy Advice Team (HEAT) has the power to test is whether yoghurt can keep you cool during the summer!
Now we don’t mean plastering yourself with yoghurt - though if you want to try this, please do send us a video as we always appreciate a good laugh. Rather, we’re talking about the viral videos doing the rounds on social media, which claim that painting yoghurt on your windows can keep your home cool during summer.
The idea goes that the yoghurt acts as a reflective shield on your windows, lowering the thermal gain experienced by your house, and keeping the internal temperature down.
Our HEAT team conduct free in-person home visits, with thermal imaging cameras, to advise Surrey residents on how to improve their homes energy efficiency, cutting bills, keeping them free of damp and mould so they stay healthy, and how to contribute to tackling climate change. (You can apply to see if you're eligible for a free visit by clicking this link).
We’ve got the equipment and knowledge to carry out a fact finding - if a little unscientific - mission on this, so our HEAT coordinator Anna grabbed a pot of yoghurt and put the theory to the test, so that we can tell you whether it’s worth doing!
Why Paint Your Windows With Yoghurt?
It’s a sensible question to ask yourself! As we said above, the yoghurt could potentially act like a heat shield on your windows, preventing thermal gain inside the property.
But couldn’t you just use radiator reflective foil or something similar? You absolutely could, and it might have better heat reflecting properties - but it doesn’t let light through. And although most of us don’t want to swelter in 30°-40°C degree heat, we also probably don’t want to be sat in darkness during the summer if we can avoid it.
So, Does Yoghurt On Your Windows Really Keep Your House Cool?
To test this out, Anna painted one of her windows with yoghurt, left the other one un-yoghurted, then broke out the thermal imaging camera to see what happened!
Watch this very short video to see the results!
Before painting with yoghurt both panes of door glass were performing roughly the same in terms of thermal gain. The yoghurt was then painted on with a standard paint mini foam roller - you can see in the image below that the right hand window has been covered with yoghurt, whereas the left hand window remains uncoated.
Now thermal imaging is more complicated than simply looking at the colours in frame. But to keep this fairly simple, the obvious first lesson is that the more red / white something is, the hotter it is. Conversely, the darker blue areas are the coldest things in frame. The colours are relative to each other, so it doesn't necessarily mean that anything dark blue is very cold, it's just the coldest thing in the shot. For example the coldest thing in an image of the inside of your home could be 20°C, but if there is a radiator in the shot, which could be 55-60°C, the material at 20°C would show up dark blue - even though it's not particularly cold.
Lesson aside, what we can see in the images is quite striking, with the door coated in yoghurt measuring around 6°C colder than the unpainted door!
The image on the right shows the temperature of the floor behind the windows (on the inside of the house). You can see a whopping difference on 19°C between the dark blue area to the right, behind the painted non-opening window pane, and the unpainted door on the left. Now we can't fully infer the reduction in thermal gain, and therefore how much lower the temperature in the house is simply from this picture. For example, if you look at the transition across the floor it looks likely that the angle of the sun is also contributing to the pattern, and that the bottom right area is potentially shielded from the sun more than the left hand area.
But we can judge pretty clearly that the door painted with yoghurt is having an effect on keeping the room cooler, and is definitely reflecting some of the heat passing into the room through the non-painted window!
Does It Smell?
No! This surprised us, but after 4 or 5 days there was absolutely no smell. There were also no flies hanging around, so top marks in terms of hygiene. The only slight caveat is that Anna caught her cat licking the window on Day 1, so perhaps keep your pets away until the yoghurt dries!
Benefits of Painting Yoghurt on Your Windows
2024 was the warmest year on record globally. January 2024 was the first time that Surrey Fire And Rescue have had to deal with a wildfire in January!
Nearly 50,000 people died in Europe in 2023 as a result of heat death. In 2022 we experienced the highest temperature ever recorded in England, a life threatening 40.3°C, and in fact across the 5 episodes of excess heat we experienced during the summer of 2022, there were an estimated 2,258 to 3,712 heat related excess deaths. Temperatures this high affect us all, not just the vulnerable - our bodies just aren’t cut out to function in temperatures this warm, and this was evidenced by significant excess deaths being observed in the 45 to 65 year age bracket in the 4th of 2022’s excess heat episodes.
Yoghurt isn’t going to help the driving factors of course. We need a rapid and managed transition away from fossil fuels to ensure a secure future for our children and young people, and we all have a part to play in this, through our home energy choices and choosing to travel by private vehicle less frequently, to how much we push government and local authorities to increase their ambitions on protecting the people and places we love.
But when temperatures reach this high, this might just be one of a number of tips that helps you to stay cool.
What’s The Verdict?
So yes, the conclusion of this blog-hurt is that coating your windows with yoghurt really can help to keep the heat inside your home down. As you can see from the video, it washes off very easily, and you can do it for a couple of quid’s worth of yoghurt, plus an old paint tray and roller, yoghurt is a cheap solution to staying cool at home during a heatwave.
It will likely wash off in rain, so you may need to reapply, and you may get a few funny looks from the neighbours (maybe apply in the cover of darkness?) but for a few minutes work, £2, and X temperature decrease we think it’s worth it!
You could also come along to our Keeping Your Home Cool Workshop to find out more simple and cheap ways to keep your home cool. Or if that doesn't suit you, we will be running a How to Keep Your Home Cool in Summer – Online Talk that will also be recorded and sent to those who have registered for it. Lastly, you can book a FREE home energy visit so that you keep your home cosy in winter and cool in summer, and find out if there’s any grant funding available to help you!
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