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How to Sleep Well in the Heat: Summer 2026 Guide

The Portuguese summer is on its way. In 2026, prolonged heat is again expected in Lisbon, the Algarve and the interior. This guide brings together what you need to keep sleeping well in the heat, based on sleep physiology and tested equipment.

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

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

If you are in the middle of a heatwave and just want the essentials for tonight, go straight to the 7 adjustments for tropical nights.

Contents

  1. Why it is harder to sleep in the heat
  2. Ideal bedroom temperature
  3. Equipment that makes a real difference
  4. How to cool the bedroom without air conditioning
  5. How to use air conditioning efficiently
  6. Summer bedding
  7. What to wear to sleep in the heat
  8. Strategic hydration
  9. The specific case of babies
  10. 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 falls by around 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), that 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) drops by 40-60% in rooms at 27°C compared with rooms 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 falls 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 drop 5-7 degrees without AC. See section 4. For the 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

A breathable mattress

Pocket springs circulate air far better than memory foam. If your current mattress is 100% foam and you sleep hot, consider moving to springs. Examples from the Dreamura range: Mizu Mattress (springs, high breathability) or Sora Mattress (springs + high-resilience foam).

A cooling pillow

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

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

A breathable mattress topper

If you cannot change the mattress, a mattress topper in a breathable fabric can help significantly. See the Nemuke Mattress Topper.

Ceiling or pedestal fan

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

What is not worth much

"Gel pack" pillows put in the freezer before bed: the effect lasts 10-20 minutes. Cooling wristbands: minimal scientifically validated effect. "Cooling" bed sheets advertised on social media: mostly marketing, with no performance difference from ordinary cotton.

4. How to cool the bedroom without air conditioning

A sequence of actions through the day to reach night-time 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 and 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 outdoor temperature drops below the indoor one, open every window
  • Create cross-draughts, ideally by opening opposite sides of the house
  • Fans pushing cool air inwards

Before going to bed

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

5. How to use air conditioning efficiently

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

Setpoint temperature

18-20°C is ideal. Each extra 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 you fall asleep. Deep sleep happens in the first hours — that is when you need the AC. After that, the room is already cool and your body temperature has already dropped.

Quiet mode

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

Airflow direction

Airflow directly onto the body causes nasal dryness, eye irritation and muscle aches 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 hold 40-50% humidity. Healthy mucous membranes, better sleep.

6. Summer bedding

Materials in order of breathability (coolest first):

  1. Linen — the most breathable. A larger investment, lasts decades.
  2. Long-staple cotton (percale) — an excellent compromise. Most Dreamura bed sheets.
  3. Tencel/lyocell — eucalyptus fibre, very cool, dries quickly.
  4. Bamboo — breathable and naturally antibacterial.
  5. Standard cotton — acceptable.
  6. Sateen — looks good but is warmer than basic cotton. Avoid in the hottest months.
  7. Polyester and synthetic blends — avoid. They do not breathe and they trap sweat.

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

Summer duvet

Swap the winter duvet for a light one (150-200 g/m² against 300-400 for winter). On very hot nights, a cotton top sheet is enough.

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 — 70% of body heat release happens through the feet and head. Feet outside the sheets, always.
  • Hair tied up if it is long. It reduces sweat on the neck.

8. Strategic hydration

The balance:

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

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

9. The specific case of babies

Babies are particularly sensitive to overheating. Paediatric recommendations:

  • Room between 18-20°C — even more critical than for adults
  • Dress the baby in 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 and feet, which are always cooler)
  • If the baby is sweating, they are overdressed or the room is too warm
  • A 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. Read our 2026 baby sleep guide for the safety detail.

10. Frequently asked questions

Does a cold shower before bed help?

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

Is sleeping naked cooler?

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

Is pointing a fan at the bed bad?

It can cause dry eyes, a sore throat and muscle aches if it blows directly onto 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 bed sheets).

Can I put bed sheets in the freezer before going to 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 out my skin?

It can dry skin and mucous membranes. Offset it with a humidifier in the bedroom, body and nasal moisturiser before bed, and by not pointing the AC directly at you.

Conclusion

Sleeping in the heat in Portugal is a seasonal problem but it does not have to be inevitable. Combining daytime habits (curtains closed, night-time ventilation) + the right equipment (breathable mattress, cooling pillow, natural-fibre bed sheets) + behavioural adjustments (warm shower, feet out, light pyjamas) solves most of it even without air conditioning.

If you are getting ready for summer and want to review your bedroom setup, talk to our Sleep Consultant, Ana Cristina — she helps work out what is worth changing and what you can keep.

Have a good summer.

See also

See also: Shinsen Pillow · Mizu Mattress · Bed Linen

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