How to Sleep Well in the Heat: Summer 2026 Guide

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

Deep sleep only happens when core body temperature falls by around 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 fell asleep".

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 developed in detail in the sections that follow.

1. 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 outdoor temperature finally begins to drop.
2. A warm shower before bed — not a cold one. Cold water closes the vessels at the surface and traps heat inside. A warm one does the opposite: it dilates the vessels and helps the body release heat once in bed.
3. Feet outside the sheet. We lose a great deal of heat through the extremities. It is the simplest gesture on the list and it has a real effect.
4. Swap synthetics for cotton or linen. Synthetic sheets retain heat and moisture against the skin. Natural fibres let air circulate and absorb perspiration better.
5. Rethink what is underneath the body. Memory foam moulds well, but it retains heat. A pocket spring mattress lets air circulate beneath the body. The Mizu (水, "water") was designed this way — pocket springs + high resilience, without memory foam.
6. The pillow is where the head heats up first. The nape is one of the first places to warm up, and a pillow that accumulates heat wakes you without you understanding why. The Shinsen (新鮮, "fresh") regulates temperature through the night, with 100 nights of trial at home.
7. Take care of the rest of the ritual. On hot nights the small mistakes weigh more: caffeine at the end of the day, screens until late, alcohol before bed. A simple, consistent ritual helps the body switch off despite the temperature.

The first four require buying nothing. Start there tonight.

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 bed linen
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, there is peripheral vasodilation (hands and feet warm up) in order to release heat. Core temperature falls by around 1 degree (37 °C → 36 °C), and it is that fall that signals to the brain: "you may fall asleep".

On hot nights (above 24 °C in the bedroom), this fall 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

Result in the laboratory: 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 falls dramatically

In the Portuguese summer, keeping the bedroom at 17-19 °C generally requires air conditioning. But there is a great deal you can do to lower it by 5-7 degrees without AC. See section 4. For full detail on this point, see the 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 feel warm, consider moving to springs. Examples from the Dreamura range: Mizu Mattress (springs, high breathability) or Sora Mattress (springs + high resilience). If you want to understand the difference between the two structures, see pocket spring or memory foam mattress.

A cooling pillow

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

• Shinsen Pillow — a 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 sleep position, see the complete guide to choosing the ideal pillow.

A breathable mattress topper

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

Ceiling or pedestal fan

It does not lower the temperature but it speeds up the evaporation of sweat, creating the 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: an effect of 10-20 minutes. Cooling wristbands: minimal scientifically validated effect. "Cooling" sheets advertised on social media: most are marketing, and do not perform differently from normal cotton.

4. How to cool the bedroom without air conditioning

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

Morning (7 am-10 am)

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

Midday (10 am-6 pm)

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

Late afternoon (6 pm-10 pm)

• When the outdoor temperature falls below the indoor one, open all the windows
• Create cross-currents — ideally by opening opposite sides of the house
• Fans pushing cool air inside

Before bed

• A warm 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:

Setting temperature

18-20 °C is ideal. Each degree higher consumes 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 occurs in the first hours — that is when you need the AC. After that, the bedroom is already cool and your body temperature has already fallen.

Silent mode

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

Direction of the flow

Direct flow 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 maintain 40-50% humidity. Healthy mucous membranes, better sleep.

6. Summer bed linen

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

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

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

Summer duvet

Replace the winter duvet with a light one (150-200 g/m² against 300-400 for 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 underwear in cotton or linen. 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 part 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 at the neck.

8. Strategic hydration

Balance:

• Enough hydration during the day (2-3 L) in order to sweat properly (sweat cools the body)
• Reduce liquids 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
• 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 1 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 the hands or feet, which are always cooler)
• If the baby is perspiring, 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 (sudden infant death). Read our baby sleep guide 2026 for safety details.

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 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 the 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 out 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 (a breathable mattress, a cooling pillow, natural fibre sheets) and behavioural adjustments (a warm shower, 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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See also

• Ideal bedroom temperature for sleeping
• Pocket spring or memory foam mattress: which to choose?
• Resting naturally begins with the pillow
• Sleep Hygiene: 12 Habits for Better Sleep
• Baby Sleep: A Complete Guide for Parents

Explore: Shinsen Pillow · Mizu Mattress · Bed Linen