Do cooling mattress pads, sleep masks and sheets help you sleep? What the evidence shows

Why body heat and falling asleep are linked

Federal guidance advises a cool, dark, quiet bedroom². The mattress-cover study that found sleep-stage gains in subgroups was funded and run by the manufacturer, and it wasn’t randomized⁴. An independent randomized trial found people rated their sleep better, but tracker-measured sleep didn’t change⁵.

Blinded one-night trials of a heat-absorbing mattress found a small gain in deep sleep⁶. Most of the eye-mask evidence comes from intensive care⁹.

Core body temperature reliably starts to fall about two hours before sleep onset, according to a 2019 narrative review of research on temperature and sleep. People who pick their own bedtime most often choose the point where it’s dropping fastest. Blood vessels in the hands and feet widen to release heat, and the review says this is usually considered part of that decline. Studies by Kräuchi and colleagues, cited in the review, found this widening was a good predictor of falling asleep. It could be seen up to two hours beforehand¹.

The same review makes a counterintuitive point: warm skin, not a cooler core, appears to help bring sleep on. In laboratory studies using a thermosuit, changing skin temperature by only about 0.4 °C within the 31 to 35 °C range shortened the time to fall asleep. Core temperature didn’t change. The review says this can encourage deeper sleep in older adults with insomnia¹.

The review’s authors also write that cooling of the body and brain hasn’t been shown to start sleep on its own. They describe it instead as a consequence of the blood vessels widening¹. The review doesn’t give sample sizes for the human studies it describes, so it’s hard to judge their strength from it¹.

For the room itself, the review cites older studies that put the best bedroom temperature at about 19 to 21 °C (66 to 70 °F). At that temperature, sleepers aim for a skin microclimate of about 31 to 35 °C under the bedding. The review says moving outside that range harms sleep¹. Federal guidance from the National Heart, Lung, and Blood Institute (NHLBI) puts it more simply: keep the bedroom quiet, cool and dark².

Warming the body before bed may work through the same heat-loss pathway. A 2019 systematic review and meta-analysis found 17 eligible studies, and 13 could be pooled. Warm showers or baths at 40 to 42.5 °C (104 to 108.5 °F) were associated with better self-rated sleep quality and sleep efficiency. A bath or shower 1 to 2 hours before bed was linked to falling asleep sooner, even one lasting about 10 minutes³.

The authors propose that extra blood flow to the palms and soles helps the body shed heat and lower its core temperature. They call for more research on the best timing, duration and mechanism³. NHLBI also lists a hot bath before bed among its sleep tips².

Do cooling mattress pads and covers improve sleep?

We found two studies of an active bed-temperature system, and both tested Eight Sleep’s Pod. It’s a mattress cover that circulates water set between roughly 13 and 43 °C^{4, 5}. In the manufacturer’s study, the settings ran in three phases: falling asleep, the next four hours and the rest of the night⁴.

The first study was funded and run by the manufacturer. Nine of its ten authors listed Eight Sleep, Inc. as their affiliation, and the tenth was a paid consultant to the company. It wasn’t randomized. The analysis covered 54 of the 75 adults recruited. Those analyzed were aged 21 to 74 (mean age 36), and half were women⁴.

Participants slept at home and chose their own settings. The cover was installed but switched off for two nights, then on for a week, then off again for two nights. Sleep stages were measured on eight nights, four with the cover off and four with it on, using a single-channel EEG home sleep test. Heart rate was measured with a Fitbit⁴.

Overall, total sleep time, sleep efficiency and time to fall asleep didn’t change significantly. Minimum sleeping heart rate fell by 1.2 beats a minute, and heart rate variability rose by 2.0 ms. Both returned to baseline once the cover was switched off again⁴.

The researchers then split nights by whether the chosen setting was cooler or warmer than the median. On nights with cooler settings in the first four hours, men gained 14.3 minutes of deep sleep (22%). In the same analyses, women gained 9.2 minutes of REM sleep⁴.

Warmer settings late in the night went the other way. Men had 23.4 more minutes of light sleep and about three more awakenings. Women spent about 8 more minutes awake⁴.

The second study was independent. It was funded by an internal research grant from La Trobe University in Australia, and its authors declared no conflicts of interest. It randomized 34 healthy, physically active adults, 20 of them women, with a mean age of 30. Using a Pod 3 cover, each person spent seven nights with the temperature feature on and seven with it off, in counterbalanced order⁵.

With the cover on, participants rated their sleep as calmer, easier to fall into, more refreshing and more satisfying. Weekly sleep-quality ratings were higher by a large margin (Cohen’s d 0.92). But sleep measured with a Fitbit wrist tracker didn’t change. There were no significant differences in total sleep time, time to fall asleep, time awake after falling asleep or sleep efficiency⁵.

The cover’s own sensors recorded heart rate, heart rate variability and breathing rate, and none changed significantly. Heart rate was about 1 beat a minute lower, which fell just short of significance. Participants knew which condition they were in. The authors write that the better ratings may partly reflect expectancy or placebo effects⁵.

A separate line of research tests passive mattresses that draw heat away from the body. A 2024 pooled analysis combined three randomized, blinded crossover studies in 72 healthy adults described as normal sleepers: young men, middle-aged men and postmenopausal women. Participants spent one night on a mattress with a high-heat-capacity polyurethane-coated top and one night on regular memory foam. Sleep was measured with full laboratory sleep recordings, in a room held at 21 to 23 °C⁶.

The coated mattress surface averaged 2.8 °C cooler through the night. Sleeping on it was linked to 7.5 more minutes of slow-wave sleep over 7.5 hours, a small effect (d 0.35). It was also linked to a heart rate 2.36 beats a minute lower. One author was affiliated with the company that made the coating, although the paper declares no competing interests⁶.

Does blocking light with a sleep mask help?

Light in the bedroom during sleep can change physiology. A Northwestern University laboratory study funded by the National Institutes of Health tested this in 20 healthy adults aged 18 to 40. After a first night in dim light, they were randomized to sleep one night under 100 lux of overhead light or in dim light under 3 lux⁷.

In the lit group, next-morning insulin resistance (HOMA-IR) rose about 15%, against a 4% fall in the dim group. Their heart rate also rose more across the night. Compared with the dim group, they spent proportionately more of the second night in light (stage N2) sleep and less in slow-wave and REM sleep. Melatonin didn’t differ. The authors note the relatively small sample and that only a single night of light was tested⁷.

That study didn’t test eye masks⁷. For masks used at home, the direct evidence is small and short. A 2023 study analyzed 89 adults aged 18 to 35. They spent a week wearing a light-blocking eye mask each night and a control week with no mask or a mask with holes over the eyes, in counterbalanced order. With the light-blocking mask, they scored slightly higher on a paired-associate learning test (episodic encoding) and had slightly faster reaction times on an alertness test⁸.

A second experiment in 33 analyzed adults of the same age repeated the learning benefit, which was only just statistically significant. That benefit tracked time spent in slow-wave sleep, measured with a wearable EEG headband. The alertness result didn’t repeat. The mask didn’t change sleep duration, sleep quality or time spent in each sleep stage⁸. The study measured memory and alertness, not health outcomes, and only in young adults⁸.

The most systematic evidence comes from intensive care units: a Cochrane review of 30 trials with 1,569 critically ill adults. It found low-certainty evidence that earplugs, eye masks or both added about two hours of total sleep. That estimate came from two studies with 116 participants (mean difference 2.19 hours, 95% CI 0.41 to 3.96). There was also low-certainty evidence that they lowered the incidence of delirium, from two studies with 177 participants (risk ratio 0.55, 0.38 to 0.80)⁹.

Most studies that measured sleep objectively found no benefit, which the review rated as very low certainty. Adverse effects weren’t clearly reported⁹. Intensive care is a very different setting from a home bedroom, so these results may not carry over.

NHLBI’s guidance is practical rather than product-based. It advises keeping the bedroom dark, using a dim night light if you need one, and avoiding bright light from TVs and computer screens in the hour before bed. If you work shifts and sleep during the day, it suggests reducing light and sound, for example with light-blocking curtains².

Do cooling sheets work? Almost no direct evidence

Sheets and sleepwear are often marketed as cooling or temperature-regulating, but controlled sleep studies are scarce. We found only one. It followed 17 healthy young adults (mean age 25) over eight test nights in a sleep laboratory, in random order and with full sleep recordings. The nights varied sleepwear (cotton or merino wool pajamas), duvet (polyester or wool) and room temperature (17 or 22 °C)¹⁰.

Wool sleepwear was linked to falling asleep faster overall. The difference was concentrated at 17 °C (about 9.9 versus 18.1 minutes). There was none at 22 °C, where wool was instead linked to a smaller share of deep (N3) sleep than cotton. The duvet fabric had no significant effect on any sleep measure, and the authors note the small sample¹⁰.

The study was funded by Australian Wool Innovation, and two of its five authors worked for the organization. It didn’t compare sheet fabrics¹⁰. The bed-surface studies above suggest that what lies directly under the body can change how much heat it loses. But they used a water-circulating cover or a specially coated mattress, not ordinary bedding^{4, 6}. We found no trials backing claims that a particular sheet weave or fiber improves sleep.

What the evidence doesn’t show

The physiology linking heat loss to falling asleep is well described, but evidence for the products built on it is thin. These gaps are why we rate the evidence weak.

• No long-term or health-outcome trials. The bed studies lasted from one night to one week. They measured sleep stages, heart rate and ratings, not longer-term health^4–6.
• Measured sleep didn’t consistently improve. In the independent Pod trial, tracker-measured sleep didn’t change⁵. In the manufacturer’s study, total sleep, sleep efficiency and time to fall asleep didn’t change overall. Its sleep-stage changes depended on sex and time of night⁴.
• No sham control or blinding for active systems. Participants in the independent trial knew when the cover was on⁵. The manufacturer’s study wasn’t randomized⁴.
• Consumer-grade measurement. The Pod studies used a Fitbit or a single-channel home EEG rather than full laboratory sleep recordings^{4, 5}. The independent trial notes that the cover’s own breathing-rate readings hadn’t been externally validated⁵.
• Narrow populations. The manufacturer’s study excluded people with insomnia, restless legs syndrome, an apnea-hypopnea index above 30 or a pacemaker⁴. The independent trial excluded people with diagnosed sleep disorders, and its participants averaged 30 years old. Its authors call for research in older adults and people with spinal cord injuries⁵.
• Industry ties. The Pod study with the most favorable objective results was funded by Eight Sleep and written mostly by its staff⁴. One author of the mattress study came from the coating maker⁶. The fabric study was funded by the wool industry¹⁰.
• Mask evidence comes from very different settings or narrow groups. The strongest data come from intensive care and are low certainty⁹. The healthy-adult trial included only 18- to 35-year-olds and measured learning and alertness⁸.
• The bedroom temperature figure rests on older studies. The often-quoted 19 to 21 °C range comes from studies cited in a review that doesn’t report their sample sizes¹.

Safety

These points come from federal guidance and from the groups the studies left out. They’re not a substitute for advice from a clinician who knows your health.

• Babies: NIH’s Safe to Sleep campaign warns that overheating, including from too many layers of clothing and bedding, raises the risk of SIDS and heat-related death. It advises dressing babies for the room temperature and keeping the head and face uncovered. It also advises a firm, flat surface with only a fitted sheet and no soft bedding. The campaign states that no product can prevent SIDS¹¹. All three bed-temperature studies above enrolled adults only^4–6.
• Heated bedding: in July 2026 the US Consumer Product Safety Commission (CPSC) told consumers to stop using one brand of electric heated blanket. Its internal heating wires could overheat and melt through the fabric. The warning followed five reports of smoking, melting or burning, including one burn injury. The maker hadn’t responded to CPSC’s requests for a recall. CPSC asks consumers to report incidents at SaferProducts.gov¹².
• Groups without data: the manufacturer’s Pod study excluded people with pacemakers or those taking beta-blockers⁴. The independent trial excluded pregnant people⁵. Neither study offers safety or benefit data for them.
• Masks and earplugs: the Cochrane review of intensive care trials found that adverse effects weren’t clearly reported⁹.
• Noise: in the independent Pod trial, 10 of 34 participants heard the cover. Of those 10, 7 said it didn’t affect their sleep, 2 said it affected it slightly and 1 said moderately⁵.

Sleep habits first, then what to look for in a bed cooling system

Federal sleep guidance focuses on habits rather than products. NHLBI advises going to bed and waking at the same times each day, with weekend times within about an hour of weekdays. It suggests a quiet hour before bed without bright screens, no alcohol before bed and no heavy meals within a few hours of it. It also advises avoiding nicotine and caffeine, which can last up to 8 hours. Its other tips are daily time outdoors and physical activity, naps of 20 minutes or less for adults, and a quiet, cool, dark bedroom².

Chronic insomnia in adults is a different matter. The American Academy of Sleep Medicine’s 2021 guideline suggests that clinicians not use sleep hygiene alone as a treatment for it. It strongly recommends that clinicians use multicomponent cognitive behavioral therapy for insomnia (CBT-I)¹³.

A bed-temperature system changes the microclimate under the body rather than the room. In the independent trial, people rated their sleep better with the cover on⁵. But across both studies, measured sleep gains were small and inconsistent^{4, 5}. If you still want one, these points follow from the studies above.

• Fine control in the mild middle: in the manufacturer’s study, participants’ median settings across the night ranged from about 23 to 29 °C (74 to 83 °F)⁴
• Small, precise steps near those settings: those medians sat far from the cover’s roughly 13 °C floor⁴, so a very wide advertised range may matter less
• Separate zones for couples: in the same study, women chose warmer settings than men in every phase of the night⁴
• A warm-up you can switch off or adjust: in the same study, late-night warming was linked to more light sleep and awakenings in men and more time awake in women⁴
• Noise: some participants in the independent trial heard the cover⁵, so ask for a decibel figure if none is published
• Caution about built-in health tracking: the independent trial notes that the cover’s breathing-rate readings hadn’t been externally validated, and the manufacturer’s own study relied on separate devices rather than the cover’s sensors^{4, 5}
• A real home trial: a return window long enough to judge comfort is worth more than claims about deep sleep, because measured benefits are uncertain and expectation can shape how people rate their sleep⁵
• Recalls and warnings: check CPSC’s recalls and warnings before you buy, since in 2026 it told consumers to stop using one brand of electric heated blanket that could overheat¹²
• Electrical safety: look for a recognized electrical safety certification mark
• Running costs: ask what water care, cleaning supplies, electricity and any membership will cost each year before you compare prices

Sources

1. The temperature dependence of sleep Frontiers in Neuroscience (Harding EC, Franks NP, Wisden W), 2019
2. Sleep deprivation and deficiency: healthy sleep habits National Heart, Lung, and Blood Institute, National Institutes of Health, 2022 · guideline
3. Before-bedtime passive body heating by warm shower or bath to improve sleep: a systematic review and meta-analysis Sleep Medicine Reviews, 2019 · meta-analysis
4. Sleeping for one week on a temperature-controlled mattress cover improves sleep and cardiovascular recovery Bioengineering (Moyen NE, Ediger TR, Taylor KM, et al.; Eight Sleep, Inc.), 2024
5. Under the covers: the effect of a temperature-controlled mattress cover on sleep and perceptual measures in healthy adults Clocks & Sleep (Stevenson S, Suppiah H, Mündel T, Driller M), 2025 · randomized trial
6. Enhanced conductive body heat loss during sleep increases slow-wave sleep and calms the heart Scientific Reports (Herberger S, Penzel T, Fietze I, et al.), 2024 · randomized trial
7. Light exposure during sleep impairs cardiometabolic function Proceedings of the National Academy of Sciences (Mason IC, Grimaldi D, Reid KJ, et al.), 2022 · randomized trial
8. Wearing an eye mask during overnight sleep improves episodic learning and alertness Sleep (Greco V, Bergamo D, Cuoccio P, Konkoly KR, Munoz Lombardo K, Lewis PA), 2023
9. Non-pharmacological interventions for sleep promotion in the intensive care unit Cochrane Database of Systematic Reviews (Hu RF, Jiang XY, Chen J, et al.), 2015 · systematic review
10. The effects of fabric for sleepwear and bedding on sleep at ambient temperatures of 17°C and 22°C Nature and Science of Sleep (Shin M, Halaki M, Swan P, Ireland AH, Chow CM), 2016 · randomized trial
11. Ways to reduce baby's risk Safe to Sleep campaign, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NIH) · guideline
12. CPSC warns consumers to stop using Melinora electric heated blankets immediately due to risk of serious injury from burn and fire hazards US Consumer Product Safety Commission, 2026 · regulator
13. Behavioral and psychological treatments for chronic insomnia disorder in adults: an American Academy of Sleep Medicine clinical practice guideline Journal of Clinical Sleep Medicine (American Academy of Sleep Medicine), 2021 · guideline