Deep foam surrounds you with insulation; springs leave space for air
A mattress feels warmer when you sink further into insulating material, so reducing that deep foam embrace is the first change I'd make. Foam insulates, and the deeper you settle into it, the more of your body is surrounded. Pocket springs leave air gaps inside the mattress. You still need to check the layers over those springs: bury them under a thick foam top and you'll spend the night against that foam.
Being too warm has a real sleep cost. In their 2012 review, Okamoto-Mizuno and Mizuno reported that, with bedding in use, heat exposure increases wakefulness and reduces slow-wave and REM sleep.2 Humid heat makes this worse. Honestly, sorting out a clammy bed is a more useful purchase decision than comparing another pair of impressive-sounding mattress names.
Heat moving away from your body matters too. In a 2018 laboratory study by Krauchi and colleagues, a high heat capacity mattress increased conductive body heat loss and slow-wave sleep compared with a conventional mattress. I take heat transfer seriously; I take a blue snowflake printed on a cover considerably less seriously.1 For shopping, the useful question is how the bed is built and how deeply you'll sink into it.
Memory foam is good at cushioning pressure and reducing movement across a shared bed. For someone who already sleeps hot, though, I think that warmth is too big a compromise, whatever cooling wording appears beside it. Deep memory foam can also feel like quicksand when you turn. Choose a more responsive surface if you want to change position without hauling yourself out of a hollow.
We asked Dr Tim Mercer, a GP partner and GP trainer, how much difference bedding makes compared with the mattress itself. His answers came back by email in October 2026.
Heat must escape through your bedding as well as the mattress, so check what you're sleeping under before blaming the bed. On a warm night, try a sheet alone: if you wake cool, the bedding was responsible, so keep the mattress. Switch to the heavier duvet after his run of cold nights, regardless of the calendar. If you're still hot under that sheet, it's the room or mattress: cool the room first, then check how the mattress is built.
The construction matters more than the cooling vocabulary
Pocket springs with wool or cotton fillings are where I start for a hot sleeper, with a thin-topped hybrid close behind. The useful differences are airflow, moisture handling and how much material surrounds you. You shouldn't need a chemistry revision session to buy a mattress, but a few material names are worth knowing.
Pocket springs: these leave air gaps beneath you, which is a useful starting point for a less enclosing bed. Look at the comfort layers as well as the spring unit. I favour pocket springs over open coil, and I care far more about what's over them than a grand spring-count announcement. A spring mattress with a deep foam top can still feel warm at the surface.
Wool and cotton fillings: these absorb and release moisture. They don't lower the temperature of the mattress; they help the bed feel dry instead of clammy. That distinction matters when you wake feeling damp. To my mind, natural fillings are a better reason to shortlist a mattress than an elaborate cooling name, especially if you dislike the close fit of foam.
Latex: this is an open-cell foam that breathes better than memory foam and doesn't soften as it warms. It feels springier, so you can move without the same slow sinking sensation. I rate latex highly for a hot, restless sleeper. The price is usually the less charming part of the introduction, so compare latex hybrids as well as mattresses with deeper latex layers.
Gel foam: gel absorbs some heat at first contact, and I think it generally makes a useful difference to the feel. This is the compromise for you if you love foam cushioning. Keep the gel foam layer relatively thin over springs, because gel doesn't remove the insulation or deep sink of the foam around it.
Cooling covers and phase-change fabrics: these can feel cool to the touch for the first minutes. I'm less convinced by them as a reason to spend more. That initial coolness is pleasant, of course, but bedtime lasts rather longer than the polite hand-patting stage in a shop. Judge the comfort layer beneath the cover before treating the fabric as a deciding feature.
Graphite: this is a heat conductor used in layers by some mattress makers. It has a practical role in moving heat, but I still want to know where the layer sits and how much foam surrounds you. Graphite would be a secondary feature on my shortlist, after the spring construction and the depth of the comfort layer.
Bamboo, Tencel and cotton covers: these feel cooler against skin than polyester and wick moisture. They're useful finishing details. Keep the rest of your bedding breathable too, because you sleep against your sheet and protector as well as the mattress cover. An appealing fabric name is a poor excuse to overlook a thick foam build.
Your duvet and protector can undo a breathable mattress
Change the bedding before replacing an otherwise comfortable mattress: a winter duvet or plastic-backed protector can leave you hot despite a spring construction underneath. Shopping for a whole new bed is rather more exciting than admitting you need a lighter duvet. Unfortunately for anyone hoping for an afternoon in John Lewis, the dull fix is worth trying first.
Reduce the duvet tog when you overheat. A lighter tog makes sense for summer, and wool-filled duvets breathe better than synthetic ones at the same tog. My heavy-duvet habit comes with a leg-out cooling arrangement, which I enjoy far more than I can reasonably recommend to someone already sweating. Choose your duvet for the warmth you need, even if the thick one looks better when you've made the bed.
The temperature next to your skin differs from the temperature of the room. Harding, Franks and Wisden's 2019 review describes sleep onset alongside a fall in core body temperature, while people use bedding to create a skin microclimate of roughly 31 to 35C.3 That is the warmth within the bedding. This is why I favour a comfortably warm bed in a cooler room, with the duvet adjusted to you.
Check the protector's backing. Plastic-backed protectors block airflow; a breathable membrane protector doesn't create the same barrier. I'm generally cool on protectors that hamper breathability. Spending carefully on a mattress and then covering it in plastic has the appeal of putting a cheap phone case over every feature you paid for. If you need protection against spills, choose a breathable membrane and check its care instructions.
Swap polyester sheets for cotton, linen or bamboo. Polyester traps heat, while those alternatives breathe. The combination matters: polyester sheets and a synthetic duvet can make a bed feel warm even when you've chosen breathable fillings underneath. Change one layer at a time if you want to work out which change makes you more comfortable.
Keep the room comfortably cool, without chasing a universal number. In Baniassadi and colleagues' 2023 longitudinal study, older adults were monitored at home using wearables.4 Sleep was most efficient at bedroom temperatures between 20 and 25C, with a 5 to 10 per cent drop in efficiency as temperature rose from 25 to 30C. The relationship was non-linear, with large differences between people. These findings were in older adults.
We also asked Dr Mercer why some people wake up too hot at night and what helps most.
His bands change with age: your parents' band is a poor guide to yours, and your adult child's is no better. Judge how you wake each morning and write it down: sweaty means less over you, chilled means more. If you share the bed with someone in a different band, favour the hotter sleeper: the colder person can add a cover when their partner has nothing left to take off. Bedding first, the room after.
I prefer a room cooler than most people initially expect, the cool end of his bands, with enough bedding to feel comfortable. Start in the band for your age, then adjust to how you sleep. A thermostat reading alone gives you very little information about the heat trapped beneath a thick duvet.
Choose the comfort layer for your body and sleeping position
Start with a spring construction, then choose enough cushioning for your shoulder and hip without sinking deeply into foam. Your body weight comes first in that decision, followed by your usual sleeping position. The firmest thing in the showroom is an unnecessarily dramatic response to feeling warm.
Read the maker's construction details for the comfort-layer material and its depth, where stated. "Hybrid" covers very different builds, so check whether you're getting a thin cushioned top or a substantial foam layer over springs. Look for wool or cotton fillings if dampness is your main annoyance. A cooling badge is much quicker to read, admittedly, but these details are more useful.
The weight bands below are rough shopping guides I use, not clinical thresholds. Brand firmness labels vary, so use the descriptions of sink and cushioning when comparing mattresses.
| Your build or sleeping habit | What to look for | What to check when you lie down |
|---|
| Lighter sleeper, under about 9 stone | A softer spring mattress or responsive hybrid with a modest comfort layer | Your shoulder and hip should settle into the surface without needing a deep foam top. |
| Hot side sleeper | Pocket springs with enough surface cushioning at the shoulder and hip; natural fillings or latex are worth trying | You should feel cushioned at those contact points without your whole side sinking deeply. |
| Heavier sleeper, over about 18 stone | A firmer hybrid with a stronger spring gauge and a thinner comfort layer | Your hips should stay supported; heavier sleepers sink further into the same comfort layer. |
| Restless or combination sleeper | A responsive spring or latex surface | You should be able to turn easily without pulling yourself out of slow-moving foam. |
For a hot side sleeper, removing all the softness is the wrong trade. Your weight is concentrated at the shoulder and hip, so you need some give there. Try a responsive comfort layer that lets those points settle while the springs support you underneath. A thin top still needs to be comfortable for your body.
Heavier sleepers sink further into a comfort layer, so more of the body is surrounded and the same mattress feels warmer. Go firmer in the support and thinner in the top if that describes you. That doesn't mean buying a thin mattress overall: a substantial spring unit with a modest comfort layer is a different construction from a shallow all-foam mattress.
In a showroom, spend a full ten minutes in the position you actually sleep in. The perched-on-the-edge performance tells you very little beyond whether your shoes match the bed. Use the visit to rule out uncomfortable pressure or excessive sink, then read the home-trial and return terms before ordering. Overnight warmth needs more time than a shop visit allows.
Avoid thick foam and heat-trapping bedding if you already run hot
Cross these combinations off your shortlist because each keeps the insulation or airflow problem in place. I wouldn't pay extra for a cooling label while ignoring what's underneath it. You can admire the embroidery for free.
- A thick all-foam mattress of any brand: deep sink surrounds more of your body with insulating foam.
- A thin gel layer over dense memory foam sold as "cooling": the initial cool touch leaves the deeper foam construction unchanged.
- A plastic-backed protector: it blocks airflow over the mattress you chose for breathability.
- A thick winter duvet kept on all year: change to a lighter tog when you overheat.
- Polyester sheets with a synthetic duvet: swap the heat-trapping combination for breathable sheets and an appropriately light duvet.
Keep the budget for construction and a workable return route. Buying a breathable mattress while keeping every heat-trapping layer is an expensive way to preserve your bedtime habits. Check what you can change on your existing bed before placing the order.
The last thing we asked Dr Mercer was when regularly waking hot or sweaty means you should see a GP, because for some of you no bed is the fix.
Book the GP before you buy a mattress if that describes you, because no new bed will put it right. Take a list of the bedding changes you've tried and your repeat prescriptions, so you can start the appointment past the easy fixes. Write down how many nights a week it happens and how long it's been going on. Keep the appointment even if a new bed is already on its way.
