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How to Sleep Well in the Heat: Summer 2026 Guide

May 23, 2026

The Portuguese summer brings nights that do not cool down — lows that stay between 20–25 °C in Lisbon, in the Algarve and inland. This guide brings together everything you need to keep sleeping well even in the heat, from the cheapest lever to the most structural one.

Deep sleep only happens when core body temperature drops by about 1 degree. On hot nights, the body cannot cool down. The result: light sleep, frequent awakenings, and that feeling of "I woke up more tired than when I went to bed".

The good news: there are many levers to pull. Some are free (habits). Others are one-off investments that last for years. This guide separates what has the most impact from what is marginal.

Shortcut: 7 adjustments for tonight

If you are in the middle of a heatwave and only want the essentials for today, start here. Each point is covered in detail in the sections below.

Close the blinds in the morning, ventilate only at night. The bedroom heats up mainly through direct light. Blinds closed during the day, windows open only after 11 pm, when the outside temperature finally begins to drop.
A lukewarm shower before bed — not a cold one. Cold water closes the vessels at the surface and traps heat inside. A lukewarm shower does the opposite: it dilates the vessels and helps the body release heat once in bed.
Feet outside the sheet. We lose a lot of heat through the extremities. It is the simplest step on the list and it has a real effect.
Swap synthetics for cotton or linen. Synthetic sheets hold heat and moisture against the skin. Natural fibres let air circulate and absorb perspiration better.
Rethink what is underneath the body. Memory foam contours well, but it retains heat. A pocket spring mattress lets air circulate under the body. The Mizu (水, "water") was designed that way — pocket springs + high resilience, no memory foam.
The pillow is where the head heats up first. The nape is one of the first areas to warm up, and a pillow that stores heat wakes you without you understanding why. The Shinsen (新鮮, "fresh") regulates temperature through the night, with 100 nights of home trial.
Take care of the rest of the ritual. On hot nights the small mistakes weigh more: caffeine late in the day, screens until late, alcohol before bed. A simple, consistent ritual helps the body wind down despite the temperature.

The first four require buying nothing. Start there tonight.

Why it is harder to sleep in the heat
Ideal bedroom temperature
Equipment that makes a real difference
How to cool the bedroom without air conditioning
How to use air conditioning efficiently
Summer bed linen
What to wear to sleep in the heat
Strategic hydration
The specific case of babies
Frequently asked questions

1. Why it is harder to sleep in the heat

The body regulates sleep through thermoregulation. As bedtime approaches, peripheral vasodilation occurs (hands and feet warm up) to release heat. Core temperature drops by about 1 degree (37 °C → 36 °C), and it is that drop that signals to the brain: "you can fall asleep now".

On hot nights (above 24 °C in the bedroom), this drop is compromised:

The air does not absorb heat from the body (reduced thermal gradient)
Sweat evaporates more slowly (high ambient humidity)
The body stays in a state of thermoregulatory alert

Laboratory result: the deep sleep phase (slow wave sleep) is reduced by 40-60% in bedrooms at 27 °C compared with bedrooms at 18 °C. It is the most critical phase for physical recovery and memory consolidation.

2. Ideal bedroom temperature

Scientific consensus:

17-19 °C — the absolute ideal, validated in multiple clinical studies
20-22 °C — acceptable, sleep moderately affected
23-25 °C — sleep already significantly disturbed
Above 26 °C — deep sleep drops sharply

In a Portuguese summer, keeping the bedroom at 17-19 °C generally requires air conditioning. But there is a lot you can do to bring it down 5-7 degrees without AC. See section 4. For full detail on this point, see ideal bedroom temperature for sleeping.

Individual differences

Women tend to need bedrooms 1-2 °C warmer than men on average. Older people regulate body temperature less well and need more thermal adjustment. Babies and small children are particularly sensitive to overheating (see section 9).

3. Equipment that makes a real difference

Breathable mattress

Pocket springs circulate air far better than memory foam. If your current mattress is 100% foam and you feel hot, consider moving to springs. Examples from the Dreamura range: Mizu Mattress (springs, high breathability) or Sora Mattress (springs + high resilience). To understand the difference between the two structures, see pocket spring or memory foam mattress.

Cooling pillow

Heat concentrates in the head. A pillow that regulates temperature can greatly reduce the perception of heat. Suggestions:

Shinsen Pillow — specific thermal regulation fabric, keeps a fresh feel all night
Sui Pillow — memory foam + cooling gel particles
Natura Toki Pillow — natural fibres (bamboo, eucalyptus), 100% cotton cover

To find the right height for your sleeping position, see the complete guide to choosing the ideal pillow.

Breathable mattress topper

If you cannot change the mattress, a topper with breathable fabric can bring significant relief. See the Nemuke Mattress Topper.

Ceiling or pedestal fan

It does not lower the temperature but it speeds up sweat evaporation, creating a sensation of 2-3 °C less. An investment of 30-150 € with immediate return.

What is worth little

"Gel pack" pillows placed in the freezer before bed: the effect lasts 10-20 minutes. Cooling wristbands: minimal scientifically validated effect. "Cooling" sheets advertised on social media: most of it is marketing, with no performance different from ordinary cotton.

4. How to cool the bedroom without air conditioning

A sequence of actions through the day to reach the night with a cool bedroom:

Morning (7am-10am)

Open everything — windows, internal doors — to create draughts with the cool morning air
Make the bed but do not cover it with the duvet (let it breathe)

Midday (10am-6pm)

Close ALL curtains and blinds, especially on the south/west side
Windows closed (the outside air is hotter)
Blackout curtains or thermal blinds: a 4-6 °C reduction in indoor temperature

Late afternoon (6pm-10pm)

When the outside temperature drops below the indoor one, open all the windows
Create cross draughts — ideally by opening opposite sides of the house
Fans pushing cool air inwards

Before bed

A lukewarm bath or shower (not cold) — vasodilation helps the body release heat
Feet and hands outside the covers (even if it is only a light sheet)
A damp towel over the pillowcase (not soaked — slightly damp)

5. How to use air conditioning efficiently

If you have AC, here is how to use it well:

Temperature setting

18-20 °C is ideal. Each additional degree uses 6-8% less energy, but sacrifices sleep quality. An acceptable compromise: 21 °C.

Timer (do not leave it on all night)

Set it to switch off 2-3h after falling asleep. Deep sleep occurs in the first hours — that is when the AC is needed. After that, the bedroom is already cool and your body temperature has already dropped.

Silent mode

AC noise can cause unconscious micro-awakenings. Use "silent" or "sleep" mode whenever available.

Airflow direction

Direct airflow over the body causes nasal dryness, eye irritation and muscle pain on waking. Point it upwards or to the side.

Humidity

AC dries the air. In very dry climates (inland Portugal in summer), consider a humidifier in the bedroom to keep humidity at 40-50%. Healthy mucous membranes, better sleep.

6. Summer bed linen

Materials in order of breathability (from the coolest to the least):

Linen — the most breathable. A larger investment, lasts decades.
Long-staple cotton (percale) — an excellent compromise. Most Dreamura sheets.
Tencel/lyocell — eucalyptus fibre, very cool, dries quickly.
Bamboo — breathable and naturally antibacterial.
Standard cotton — acceptable.
Satin — visually attractive but warmer than basic cotton. Avoid in the hottest months.
Polyester and synthetic blends — avoid. They do not breathe, they trap sweat.

Dreamura has cotton sheets across several lines. See the Bed Linen Collection or the Natura Toki pillow with a 100% cotton cover.

Summer duvet

Replace the winter duvet with a light one (150-200 g/m² versus 300-400 in winter). On very hot nights, a cotton top sheet is enough. On the right weight for each season and the size to choose, I wrote a separate guide.

7. What to wear to sleep in the heat

Light cotton or linen underwear. Avoid synthetics.
Thin cotton pyjamas or a short nightdress. Counter-intuitive, but the fabric absorbs sweat and keeps a dry feel — often better than sleeping naked.
Uncovered feet — a large share of body heat release happens through the feet and the head. Feet outside the sheets, always.
Hair tied up if it is long. It reduces sweat on the neck.

8. Strategic hydration

Balance:

Enough hydration during the day (2-3 L) to sweat properly (sweat cools the body)
Reduce fluids 2 hours before bed (so as not to wake up needing the bathroom)
A glass of water on the bedside table for small sips if you wake up
Cool water, not iced (iced water makes the body generate more heat to compensate)

Avoid at night: alcohol (it dilates vessels and dehydrates) and heavy meals (digestion generates metabolic heat).

9. The specific case of babies

Babies are particularly sensitive to overheating. Paediatric recommendations:

Bedroom between 18-20 °C — even more critical than for adults
Dress the baby with one layer less than you would be comfortable in
A light sleeping bag (0,5-1 tog) instead of blankets
Check the baby's temperature at the neck or torso (not hands/feet, which are always cooler)
If the baby is sweating, they are overdressed or the bedroom is too warm
Breathable cot mattress: the Mokuren Baby Mattress with pocket springs is more breathable than solid foam mattresses

Overheating in babies increases the risk of SIDS (sudden infant death). Read our baby sleep guide 2026 for safety details.

10. Frequently asked questions

Does a cold bath before bed help?

No. A cold bath makes the body generate more heat to compensate. A lukewarm bath is better: it causes vasodilation and helps the body release heat afterwards.

Is sleeping naked cooler?

It depends. In high humidity, sleeping naked can let sweat build up on the skin. Light cotton pyjamas that absorb sweat can be more comfortable.

Is a fan pointed at the bed bad?

It can cause dry eyes, a sore throat and muscle pain if it blows directly on the body for 8 hours. Point it at the ceiling or a wall to circulate air without direct flow.

Is it worth investing in a new mattress just because of the heat?

If the mattress is more than 8 years old OR is 100% memory foam, yes. Otherwise, start with the cheaper levers (curtains, fan, cooling pillow, linen sheets).

Can I put sheets in the freezer before bed?

Yes, but the effect lasts 15-20 minutes. On an exceptionally hot night, it is worth it. Not as a regular solution.

Does air conditioning dry my skin?

It can dry the skin and the mucous membranes. Compensate with a humidifier in the bedroom, body and nasal moisturiser before bed, and do not have the AC pointed directly at you.

Conclusion

Sleeping in the heat in Portugal is a seasonal problem, but it does not have to be inevitable. The combination of daytime habits (closed curtains, night ventilation), suitable equipment (breathable mattress, cooling pillow, natural fibre sheets) and behavioural adjustments (lukewarm bath, feet outside, light pyjamas) solves most of the problem even without air conditioning.

Not sure where to start? Take the mattress quiz or talk to me — we will look together at what makes sense for your sleep.
— Ana Cristina, Sleep Advisor · +351 21 150 95 04

First order at dreamura.com? The code WELCOME10 gives −10% on the first purchase, on orders from 150 €.

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