With the recent climate change across the country, many of us have been losing out on precious hours of sleep. We asked sleep expert Charlie Oulton ‘why is it so difficult to sleep when it’s warm outside?’ Turns out, there’s a little more to it than ‘because it’s too hot’.

Temperature and Sleep

The core temperature of our body is 36.5 degrees. Even a small fluctuation in temperature can result in illness, so our bodies work to keep the core temperature at the optimum 36.5 degrees.

You may be surprised to hear that the largest organ in the body, our skin, has a ‘thermoneutral point’ (ideal, comfortable temperature) of 27 degrees - significantly cooler than our core, but still rather warm!

This explains why we enjoy getting cosy under the covers before falling asleep (especially during the Winter). Once our skin reaches 27, we are primed and ready to drift off in to a restful slumber.

stretching wake up

The science behind it

For the best chance of a good sleep, our bedroom should be between 18-22 degrees. Here’s why:

The temperature of our bed when we climb in is ‘room temperature’, therefore (hopefully) between18-22 degrees - maybe slightly warmer during a heatwave!

Once we’re in bed, our bodies begin work to warm the bed up to our ideal temperature of 27 degrees. Meanwhile, we feel ourselves cool down because of the energy being used to heat the bed.

Here’s the interesting part. When the bed is warmed to our ideal temperature, we fall asleep - this usually takes around 15 minutes. Wouldn’t it be great if we could then sleep the whole night through at our perfect, comfortable temperature with no disturbance?

You may be familiar with the ‘leg out, leg in the covers’ cycle

sleeping without covers - too hot to sleep


  1. We are insulated by the duvet, so our bodies continue to warm up.
  2. When we hit the ‘too hot’, uncomfortable temperature, our sleep is disturbed and most of us wake up and either stick one leg out of the covers, or kick them off completely.
  3. Now, more of our skin is exposed to the cooler air, and our temperature drops - often dropping below the ideal 27 degrees - and, you guessed it:
  4. We wake up to find the covers and get cosy again!

This cycle continues throughout the night, leading to a groggy, miserable next morning after a night of poor, interrupted sleep.

Does my mattress contribute to hot, uncomfortable nights?

There’s a well known viewpoint that foam mattresses are ‘hotter’ than sprung mattresses.

Whilst this may hold some truth, it’s not quite that simple…

It’s not the foam mattress to blame, but rather the specific type of foam (visco-elastic) which is found in memory foam mattresses.

Memory foam is softened by heat, and so when we warm up, we sink further in to the foam. Some sink is good as it supports the body over a greater area and decreases pressure - giving the feeling of weightlessness.

Too much sink however makes it difficult for air to flow through the mattress, resulting in it feeling even warmer due to the air escaping from the millions of tiny holes. The additional sink also makes it difficult to turn over and can become uncomfortable over time.

Don’t all foam mattresses use memory foam?

Simply put, no! Memory foam is the most common foam used in mattresses, but there is a far more superior solution which has all the benefits of memory foam, without any of the downsides.

Reflex foam is made with larger bubbles. Instead of reacting to heat, it reacts to pressure. When pressure is applied, the bubbles are displaced and pushed ‘sideways’, but the air doesn’t escape - meaning the air can still flow through the mattress. These bubbles mean that reflex foam bounces back to its’ original shape once the pressure is relieved, whereas memory foam may take a while to return back.

It’s not what’s underneath, but what’s on top that counts

The mattress you sleep on is 9-10 times less important than what’s on top when it comes to heat and sleep. The duvet we choose plays a vital role in determining whether we sleep well, or sleep poorly.

Sleep cool with these hacksSleeping cotton pyjamas summer

  1. Wear loose fitting, cotton pyjamas - cotton helps to wick away moisture for a refreshing sleep.
  2. Choose cotton sheets - they’re breathable and comfortable.
  3. Switch to a lower tog ‘Summer’ duvet - or ditch the duvet altogether and use a sheet.
  4. Keep curtains and blinds closed during the day.
  5. Use an electric fan - place an iced bottle or bowl of water in front for even cooler air flow.
  6. Open windows for a breeze - if there is one outside!
  7. Have a cool shower - not cold though as that would be stimulating.
  8. Stay still! Try not to get frustrated about the heat - it will only make you feel even hotter.
  9. Avoid eating or drinking about 2 hours before bedtime - but take some water to bed with you.
  10. Avoid memory foam mattresses - if you like the comfort of foam, try a reflex foam mattress instead like the DUO or Nrem.

DUO mattress reflex foam