Why Is My Mattress Topper So Hot? Causes and Fixes
A topper that sleeps hot is usually trapping heat in the foam, its cover, the protector or the sheets. How to find which, and what to change first.
Research-based: public sources and consumer feedback, not hands-on testing. How we review
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In this article
Quick Verdict
Better alternatives availableBottom line: Most toppers that sleep hot are memory foam, and the foam itself is the main cause. Change the room, the protector and the sheets first; if that fails, a different material is the fix.
- Main concern
- Thick, soft memory foam if you already sleep warm
- Better alternative
- A ventilated latex or wool topper
Research-based: public sources and consumer feedback, not hands-on testing. How we review
Quick answer
A topper usually feels hot because memory foam softens around your body and leaves little room for air to move, so the warmth you give off stays next to you. Before you replace it, check the layers on top of it: a waterproof protector or synthetic sheets can add to the problem, and both are cheaper to change than the topper.
You bought a topper to make the bed more comfortable, and now you wake in the small hours with the covers kicked off. Heat is the drawback that independent bedding guides raise most consistently with foam toppers, and they are fairly consistent about where it comes from. This guide works through the possible causes one layer at a time, starting with the ones that cost nothing to fix.
If you have not bought yet, our mattress topper buying guide explains which materials and thicknesses suit warm sleepers in the first place.
Key takeaways
- Memory foam softens with body heat and molds closely, which limits the air moving around you
- Denser foam and softer foam both tend to hold more heat, and so does sinking further in
- The topper's own cover, a waterproof protector or synthetic sheets can each add warmth
- Sleep Foundation's reviewers say the jury is out on how much gel infusions help
- If the cheaper changes fail, ventilated latex, wool and down alternative are the types its testers find coolest
Work out which layer is trapping the heat
A made bed is a stack: mattress, topper, the topper’s cover, often a protector, then a fitted sheet, then you. Any of those layers can hold warmth. The topper gets the blame because it is the newest thing on the bed, but it is worth ruling out the others before you spend money.
Where the Heat Is Coming From
Each cause below is taken from published guidance by independent bedding reviewers. They describe how materials behave in general, not any one product.
The foam molds around you
Memory foam becomes more pliable as your body heat warms it, which is why it feels softer once you have been lying on it for a while. The same property means it closes in around you. The Sleep Foundation notes that because the foam is dense as well as heat-responsive, it can trap warmth and become uncomfortable, traditional memory foam in particular.
Dense foam, or very soft foam
Denser foams keep their shape for longer but usually hold more heat. Softness matters as well: the further you sink, the more of your body is surrounded by foam, and heavier sleepers sink further still. For that reason the Sleep Foundation suggests that people who run hot may do better on a firmer topper.
The topper's own cover
A breathable core does not help much if it is wrapped in fabric that blocks air. The Sleep Foundation’s testing notes point out that a topper inside a cover that restricts airflow can still run warm.
Source: Sleep Foundation: Mattress Topper Research Methodology
A waterproof protector on top
Many people put a protector over a new topper to keep it clean. The waterproof layer in a protector can limit airflow and let heat build up on the sleep surface, although manufacturers design these products to let through as much air as they can.
Sheets that do not breathe
Synthetic fibers are less breathable and trap more heat at night. Weave matters too: sateen is heavier and holds more warmth than percale, while flannel, fleece, jersey and microfiber are aimed at people who sleep cold.
A warm bedroom
Your core temperature falls by about two degrees Fahrenheit overnight, and a cool room helps that happen. The Sleep Foundation’s medically reviewed guidance gives 65 to 68 degrees Fahrenheit (about 18 to 20 Celsius) as the range most doctors suggest. The same topper is likely to feel warmer in a bedroom well above that.
What to try, cheapest first
Change one thing at a time and give it a few nights, so you can tell what made the difference.
- Cool the room. Turn the thermostat down at night, use a fan or air conditioning, and keep blinds closed during the day so the room does not store heat. These are the Sleep Foundation’s first suggestions, and they cost little or nothing.
- Take the protector off for a few nights. This is a simple test of our own, not something from a study: if the bed is clearly cooler without it, the protector was part of the problem. Look for one sold as breathable, or go without waterproofing if you do not need it.
- Change the sheets. Cotton percale, linen, bamboo-derived viscose and Tencel are the fabrics the Sleep Foundation describes as breathable. If yours are sateen, microfiber or flannel, swap them before you blame the foam.
- Look at the topper’s cover. Cotton and wool covers are breathable and wick moisture. If the cover is removable and made of a slick synthetic, try the topper under a cotton sheet without it, as long as the care instructions allow the cover to come off.
- Only then, question the topper. If none of that helps, the foam itself is the cause, and the fix is a firmer topper or a different material. Our guide to materials worth considering instead of memory foam compares the options, and our summary of cooling toppers covers the named products testers rated.
What “cooling” on the label does and does not mean
The Sleep Foundation describes “cooling” as one of the bedding industry’s main marketing words, and the features behind it vary a great deal:
- Gel is mixed into the foam or laid on top to draw heat away. The Sleep Foundation’s reviewers say the jury is out on whether it makes a real difference.
- Copper, graphite and charcoal are added for the same purpose.
- Open-cell and convoluted (egg-crate) foam is shaped to let more air pass through.
- Phase-change materials are designed to absorb, store and release heat.
- Active cooling toppers circulate air or water through the surface. They are the most expensive type.
We did not find, in any of these guides, a common measure that lets you compare one brand’s cooling claim with another’s. Treat the word as a statement of what the maker was aiming for, and look at the material and the firmness instead.
Who Can Probably Fix It With Bedding
- Sleepers who were comfortable until they added a waterproof protector
- Anyone using sateen, flannel or microfiber sheets
- People whose bedroom is warmer at night than the mid-60s Fahrenheit
Who Is Likely to Need a Different Topper
- Hot sleepers on thick, soft memory foam that they sink deeply into
- Anyone who has already changed the sheets and the protector without relief
- Buyers who are still inside the return window
If you are still inside the return window
Do not use up the return period experimenting. Topper returns are often restricted, and some brands do not accept them at all, so read the seller’s terms today and note the last date you can send it back. The buying guide lists the return questions to ask, and our guide to returns, refunds and chargebacks covers what to do if a seller refuses.
A thin quilted pad is a much smaller change to the bed than a slab of foam. If you only wanted a slightly softer surface, our comparison of a mattress topper and a mattress pad may point you to the lighter option.
How we researched this
This article is based on published guidance from the Sleep Foundation’s product testers and its medically reviewed sleep articles, and on Consumer Reports’ advice as reported by a US news station. We did not test any topper or measure temperatures ourselves, and we have not named or ranked products.
Should You Replace It?
Only after the cheaper changes have failed
If the room, the protector and the sheets are not the cause, the foam is, and no accessory will change how it behaves. The types the Sleep Foundation’s testers find best at temperature control are ventilated latex, wool and down alternative. Consumer Reports draws the same broad line: memory foam can trap heat, while latex tends to sleep cooler. Each alternative gives something up in return, usually price, weight or the close hug of memory foam.
Better choice for some buyers
A ventilated latex topper
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Frequently Asked Questions
Why is my memory foam topper so hot?
Memory foam softens as it warms and molds closely around you, so less air moves over your skin and the heat you give off stays close. Dense foam, soft foam and a deep sink all make it worse. A waterproof protector or synthetic sheets on top can add to the effect.
Does a thicker topper sleep hotter?
Not because of thickness alone. What matters is how far you sink in. A thicker foam topper contours more closely, and the more of you the foam surrounds, the more heat builds up, so a thick, soft topper is the warmest combination.
Will a mattress protector make my topper hotter?
It can. The Sleep Foundation notes that waterproof layers can limit airflow and let heat build up. Sleeping without the protector for a few nights is the quickest way to find out whether yours is doing that.
Is gel memory foam cooler than ordinary memory foam?
The evidence is mixed. Gel is added to draw heat away from the body, but the Sleep Foundation’s reviewers say the jury is out on whether it makes a real difference. Treat it as a possible small improvement, not a cure.
What temperature should a bedroom be for sleep?
The Sleep Foundation’s medically reviewed guidance says most doctors suggest 65 to 68 degrees Fahrenheit, about 18 to 20 Celsius, with some variation from person to person.
Sources & Evidence
Where the facts in this article come from. Summaries are in our own words; follow the links to check them yourself.
- Sleep Foundation: What Is Memory Foam?
- Sleep Foundation: Best Cooling Mattress Toppers
- Sleep Foundation: Mattress Topper Research Methodology
- Sleep Foundation: Best Mattress Protectors
- Sleep Foundation: Best Cooling Sheets
- Sleep Foundation: Best Temperature for Sleep
- Sleep Foundation: Best Mattress Toppers
- KOMO News: Consumer Reports, mattress topper or a new mattress? (2022)
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