If you wake up hot, kick the covers off or hang a leg out from under the duvet, the bed itself is usually the cause. Most overheating comes down to one thing: man-made fillings that take your body heat and push it straight back at you. Natural materials do the opposite. They breathe, draw moisture away and let your body cool, which is exactly what it has to do to reach deep sleep. Here is how the materials inside a mattress decide whether you sleep hot or cool, and what to look for if you run warm at night.
Why does my mattress make me sleep hot?
Quick answer: Nine times out of ten, it is what you are lying on. Foam and polyester fillings trap your body heat instead of moving it away, so the warmth has nowhere to go.
Nine times out of ten, you are lying on something with a man-made fibre inside, foam or polyester fillings. As you lie on it, it takes the heat of your body and pushes that heat straight back at you. It does not cool you down. It just gets hotter and hotter.
Memory foam is the clearest example. It is thermoreactive, so the heat of your body softens the top surface and you sink into it. That close contact feels comfortable when you first lie down, but the same surface keeps getting warmer through the night. To reach deep sleep your body needs to cool, and if it cannot, you turn over in reaction to the heat. The result is broken, restless sleep.
Heat is more destructive on a sleep pattern than even a bad mattress. Heat is what you have to control.
It is not only the mattress. Poly-cotton or satin sheets, a pillow with a synthetic filling, or a duvet that is far too thick will all hold heat against you. The bed is the place to start, but the whole sleep setup matters.
Is 'cooling gel' memory foam actually cooling?
Quick answer: No. Cooling gel is a chemical layer added on top of foam to mask a problem the foam itself creates. It does not deal with the cause.
The cooling gel is a reaction to the foam. They put it on top to try to cool you down, but the problem causing the heat is still there. It might be a short-term fix, but the wound is still there underneath.
There is a reason we have never built a bed this way. Over forty years in the industry you see every approach, including heated water beds set to body temperature. They felt wonderful to get into on a cold night, but the polyurethane bladder and the chemicals needed to keep the water clean meant they gassed off, and from a health point of view people moved away from them. A cooling gel sitting on a block of foam belongs in the same category: a man-made answer to a man-made problem.
None of this is guesswork. Your body has to lose heat to fall and stay asleep, which is why the link between a cool bedroom and good sleep is so well established, with around 18 degrees widely recommended as the ideal.
How do natural materials keep you cool?
Quick answer: They breathe. Natural fillings absorb moisture and release it, so heat and damp move away from your body instead of building up underneath you.
A natural mattress works with your body instead of fighting it. Three fillings do most of the work.
Why wool keeps you cool in summer and warm in winter
Wool is the workhorse. It is cool when you are warm and warm when you are cold, and it breathes either way. If you heat up in the night, it releases moisture rather than holding it against you. That is why the top layer of every Marshall & Stewart mattress is wool, or wool blended with cashmere. It is soft, it draws moisture away, and it keeps you even through the night.
Wool is the most fantastic filling you can use. It is cool in the summer, warm in the winter, and it breathes.
Why horsehair stops you waking up clammy
Horsehair gives a mattress its bounce and its cushioning, but it does something just as important for how you sleep. Each strand is a hollow fibre, so it draws the moisture you give off away from your skin and keeps you from waking up clammy.
This matters more than people realise. Across one night a single sleeper loses between a pint and a pint and a half of moisture. Two of you in a bed lose around three pints. A filling that moves all that away keeps you comfortable, and it keeps the sleeping surface healthy too. A warm, damp bed is where dust mites thrive, and a heavy infestation can trigger breathing problems, so good horsehair is doing far more than keeping you cool. Airing your bed during the day helps as well.
Why cashmere sits closest to your body
Cashmere is the luxury layer, and it earns its place. We blend it with merino wool and use it to surround the horsehair core, top and bottom, in our Koh-I-Noor and Cullinan mattresses. The cashmere goat survives a brutal climate, from well below freezing to real summer heat, so the fibre is built to handle swings in temperature. It also has a beautiful soft lustre and handle, which is why we keep it next to you.
Do the springs change how hot you sleep?
No. The springs give you tension and support, and they work hard carrying the weight of your body, but they do nothing for temperature. Every bit of heat regulation happens in the natural fillings above the springs. If a bed sleeps cool, it is the upholstery doing the work, not the spring unit.
Do you need a different bed for summer and winter?
Quick answer: Not if the fillings are good enough. A well-made natural mattress copes with every season, so you do not need to swap beds.
The idea of a separate summer bed and winter bed comes from older seasonal-turn mattresses, which had wool on one side and silk or cotton on the other so you could flip them with the seasons. In practice those layers are so thin they make little real difference.
A mattress with quality natural materials inside is designed to cope with everything from a few degrees below freezing to thirty or forty degrees of summer heat. You do not need two beds. If you want to fine-tune the feel by season, a summer or winter topper is a far simpler answer than changing the whole mattress.
What should I look for if I want a cooler bed?
Quick answer: Natural materials inside the mattress, a cool room, the right duvet, and natural pillows and nightwear. The bed does most of the work, but the setup around it matters too.
If you are shopping now and you tend to overheat, the rules are simple:
- Buy natural materials inside the mattress. Wool, horsehair, cashmere and cotton will serve you in every season.
- Get your room temperature right. Around 18 to 19 degrees is ideal, cool enough to let your body cool down.
- Use a fan if you need one. It moves the air and adds a little white noise, which helps you settle.
- Check your duvet tog. A 4.5 tog is a summer weight, 7.5 covers all seasons, and 9 is really for Scandinavian winters. In the UK, 7.5 is plenty and 4.5 is often better. A thick, fluffy duvet looks lovely on the bed, but it will leave you in a sauna.
- Look at your pillows and nightwear. A synthetic pillow pushes heat back at your head, just like a foam mattress. Choose natural fillings, and wear 100 per cent cotton or silk.
Can the right bed help with night sweats and menopause?
It can help, though it will not do everything on its own. If you run hot at night, the practical steps make the biggest difference: a bed wide enough that you are not sharing heat with a partner, a duvet that is not too warm, proper natural fillings underneath you, and a fan moving the air. The aim is always the same, which is to let your body cool down so it can reach deep sleep.
I was so wrapped up on price initially that I hadn't considered the price on my quality of sleep! My quality of sleep has so greatly improved that I don't want to get out of bed!
— Verified customer, Marshall & Stewart (East Sheen)
Solve support and temperature together
Quick answer: People turn in the night for one of two reasons: the bed is too hot, or it is too hard. A bed built properly solves both at once.
Get the support right for your body and the temperature looks after itself, because the natural fillings that hold you in good alignment are the same ones that keep you cool and dry. That is the whole point of a bed made this way.
None of our mattresses will make you hot. If a customer asks me for memory foam, I tell them I will never sell it to you. I would never have it in my shop.
I used to sleep on a Tempur mattress. I now sleep on a Marshall & Stewart Sancy, and the difference is chalk and cheese. The sleeping experience has improved from 0 to 100. I absolutely love it.
— Nawfel, verified customer, Marshall & Stewart
Frequently Asked Questions
Can a mattress topper fix an overheating bed?
A natural-fibre topper can help with moisture and feel, but it will not cure a foam mattress that is generating the heat underneath it. The cause sits in the mattress, not on top of it.
Is a firmer mattress cooler than a soft one?
Firmness and temperature are separate. Firmness comes from the spring tension, while temperature is decided by the fillings. A firm bed with synthetic fillings can still sleep hot.
What duvet tog is best for avoiding overheating in the UK?
For most UK homes, 7.5 tog is the warmest you need, and 4.5 is often more comfortable. A 9 tog or higher is really for very cold climates.
Do natural materials help with dust mites and allergies?
Yes. Natural fillings draw moisture away and keep the bed drier, and a dry bed is far less hospitable to dust mites, whose waste can trigger breathing problems.
What room temperature is best for sleep?
Around 18 to 19 degrees. It is cool enough to let your body lower its core temperature, which is what it needs to do to reach deep sleep.
Visit us
If you are tired of waking up hot, the best thing you can do is feel the difference for yourself. Visit our East Sheen showroom in London, where one of our sleep specialists will talk you through how your current bed is built, why it might be overheating you, and what a natural mattress feels like to sleep on. There is no pressure and no commission, just honest advice about how to sleep cooler and better. Book your sleep consultation whenever you are ready.
