How to Sleep Well in the Heat: Summer 2026 Guide
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Portuguese summer is on the way. In 2026, prolonged heat is expected again in Lisbon, the Algarve and the interior. This guide brings together everything you need to keep sleeping well in the heat — grounded in sleep physiology and tested equipment.
Deep sleep only happens when core body temperature drops by about 1 degree. On hot nights, the body can't cool down. Result: light sleep, frequent awakenings, and that feeling of "I woke up more tired than I went to bed".
The good news: there are many levers to pull. Some are free (habits). Others are one-off investments that last years. This guide separates what matters most from what is marginal.
Table of contents
- Why it's 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 bedding
- What to wear to sleep in the heat
- Strategic hydration
- The specific case of babies
- Frequently asked questions
1. Why it's 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 that drop signals the brain: "you can fall asleep".
On hot nights (above 24°C in the bedroom), this drop is compromised:
- The air doesn't absorb body heat (reduced thermal gradient)
- Sweat evaporates more slowly (high ambient humidity)
- The body remains in a state of thermoregulatory alert
Lab result: deep sleep (slow wave sleep) is reduced by 40-60% in bedrooms at 27°C vs bedrooms at 18°C. It's the most critical phase for physical recovery and memory consolidation.
2. Ideal bedroom temperature
Scientific consensus:
- 17-19°C — absolute ideal, validated in multiple clinical studies
- 20-22°C — acceptable, sleep moderately affected
- 23-25°C — sleep already significantly disrupted
- Above 26°C — deep sleep drops dramatically
In a Portuguese summer, keeping the bedroom at 17-19°C usually requires air conditioning. But there's a lot you can do to drop 5-7 degrees without AC. See section 4.
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 much better than memory foam. If your current mattress is 100% foam and you feel hot, consider switching to springs. Examples from the Dreamura range: Mizu Mattress (springs, high breathability) or Sora Mattress (springs + high resilience).
Cooling pillow
Heat concentrates around the head. A pillow that regulates temperature can dramatically reduce perceived heat. Suggestions:
- Shinsen Pillow — specific thermo-regulating fabric, keeps a fresh feel all night
- Sui Pillow — memory foam + cooling gel particles
- Natura Toki Pillow — natural fibres (bamboo, eucalyptus), 100% cotton cover
Breathable mattress topper
If you can't change the mattress, a topper with breathable fabric can help significantly. See Nemuke Mattress Topper.
Ceiling or pedestal fan
It doesn't lower temperature but speeds up sweat evaporation, creating a feeling of 2-3°C less. Investment of €30-150 with immediate payback.
What's worth little
"Gel pack" pillows put in the freezer before bed: effect lasts 10-20 minutes. Cooling wristbands: minimal scientifically validated effect. "Cooling" sheets advertised on social media: mostly marketing, performance no different from regular cotton.
4. How to cool the bedroom without air conditioning
Sequence of actions through the day to reach the night with a cool bedroom:
Morning (7am-10am)
- Open everything — windows, internal doors — to create air currents with the cool morning air
- Make the bed but don't cover it with the duvet (let it breathe)
Midday (10am-6pm)
- Close ALL curtains and blinds, especially on the south/west side
- Windows closed (outside air is hotter)
- Blackout curtains or thermal blinds: 4-6°C reduction in indoor temperature
Late afternoon (6pm-10pm)
- When outdoor temperature drops below indoor, open all windows
- Create cross-currents — ideally opening opposite sides of the house
- Fans pushing cool air inwards
Before bed
- Warm shower or bath (not cold) — paradoxical vasodilation helps the body release heat
- Feet and hands out of the covers (even just a light sheet)
- Damp towel over the pillowcase (not soaked — slightly damp)
5. How to use air conditioning efficiently
If you have AC, here's how to use it well:
Set temperature
18-20°C is ideal. Each extra degree uses 6-8% less energy but sacrifices sleep quality. Acceptable compromise: 21°C.
Timer (don't leave it on all night)
Program it to turn off 2-3h after falling asleep. Deep sleep occurs in the first hours — that's when you need the AC. After that, the room 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.
Air flow direction
Direct flow over the body causes nasal dryness, eye irritation and muscle soreness on waking. Aim it upwards or to the side.
Humidity
AC dries the air. In very dry climates (Portuguese interior in summer), consider a humidifier in the bedroom to maintain 40-50% humidity. Healthy mucous membranes, better sleep.
6. Summer bedding
Materials in order of breathability (from coolest to least):
- Linen — the most breathable. Bigger investment, lasts decades.
- Long-staple cotton (percale) — excellent compromise. Most Dreamura sheets.
- Tencel/lyocell — eucalyptus fibre, very cool, dries quickly.
- Bamboo — breathable + naturally antibacterial.
- Standard cotton — acceptable.
- Satin/sateen — looks great but warmer than basic cotton. Avoid in the hottest months.
- Polyester and synthetic blends — avoid. They don't breathe, they trap sweat.
Dreamura has cotton sheets in several lines. See the Bedding Collection or the Natura Toki Pillow with 100% cotton cover.
Summer duvet
Replace the winter duvet with a light one (weight 150-200g/m² vs 300-400 in winter). On very hot nights, just a top cotton sheet is enough.
7. What to wear to sleep in the heat
- Light underwear in cotton or linen. Avoid synthetics.
- Thin cotton pyjamas or a short nightgown. Counterintuitive, but the fabric absorbs sweat and keeps a dry feel — often better than sleeping naked.
- Bare feet — 70% of body heat release happens through feet and head. Feet out of the sheets, always.
- Tied-up hair if it's long. Reduces sweat on the neck.
8. Strategic hydration
Balance:
- Enough hydration during the day (2-3L) to sweat properly (sweat cools the body)
- Reduce fluids 2 hours before bed (to avoid waking up to pee)
- Glass of water on the bedside table for mini-sips if you wake up
- Cool water, not iced (iced paradoxically makes the body generate more heat to compensate)
Avoid at night: alcohol (vasodilates 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
- Light sleeping bag (weight 0.5-1 tog) instead of blankets
- Check baby's temperature on the neck or trunk (not hands/feet, which are always cooler)
- If the baby sweats, they are overdressed or the room 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 syndrome). Read our baby sleep 2026 guide 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 paradoxical vasodilation and helps the body release heat afterwards.
Is sleeping naked cooler?
It depends. In high humidity, sleeping naked can let sweat accumulate 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, sore throat and muscle soreness if aimed directly at the body for 8 hours. Point it at the ceiling or 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 the sheets in the freezer before bed?
Yes, but the effect lasts 15-20 minutes. If it's an exceptionally hot night and you're desperate, go for it. Not as a regular solution.
Does air conditioning dry out my skin?
It can dry skin and mucous membranes. Compensate with a humidifier in the bedroom, body and nasal moisturisers before bed, and don't have the AC aimed directly.
Conclusion
Sleeping in the heat in Portugal is a seasonal problem but it doesn't have to be inevitable. The combination of daytime habits (curtains closed, night ventilation) + the right equipment (breathable mattress, cooling pillow, natural-fibre sheets) + behaviour adjustments (warm shower, feet out, light pyjamas) solves most problems even without air conditioning.
If you're preparing for summer and want to review your bedroom setup, talk to our Sleep Adviser, Ana Cristina — she helps identify what's worth changing and what you can keep.
Have a good summer.
See also
- Tropical summer: how to sleep well in the heat
- Resting naturally starts with the pillow
- Sleep Hygiene: 12 habits for better sleep
- Baby Sleep: Complete Parents' Guide
Explore: Shinsen Pillow · Mizu Mattress · Bedding
