13 tips to stay warm and sleep well in a tent

Sleeping outdoors, especially in mountain areas or in cold seasons, can become a challenge if you don't have the right equipment or don't know certain technical tricks. Ensuring a good night's sleep is essential to be able to perform the following day, whether you are hiking for several days in the Pyrenees or in any other mountain range. These tips, accompanied by technical information, will help you make the most of your nights under the stars.

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To know values and technical details (comfort temperatures of bags, etc.), R-Value The use of mats, characteristic of 4-season tents) can make the difference between an unpleasant night and an unforgettable experience.

1. Use a four-season tent (or one appropriate to your environment).

Why four seasons?

• Reinforced structure and rods to withstand winds of more than 50-70 km/h and moderate snowfall.
• Heavier weight fabrics offer better abrasion and tear resistance.
• In the data sheet of a 4-season tent, look for:
  • Water resistance (water column): minimum 3000 mm in double-ceiling and 5000 mm on the ground for winter mountaineering (some tents even reach 8000 mm).
  • Good ventilation system to avoid internal condensation.

At altitudes above 1500-2000 metres in Pyreneesat night, night temperatures may drop below -5 ºC in winter the best of days. Keep this in mind when choosing your tent.

2. Choose a sleeping bag with the right comfort temperature.

The EN 13537 standard (or ISO 23537 as updated) provides a unified temperature classification for sleeping bags:

• Comfort Temperature (Tcomfort)temperature: the temperature at which a "typical" person sleeps relaxed without getting cold.
• Temperature Limit (Limit)The minimum temperature at which an average user can sleep huddled together without feeling excessively cold.
• Extreme Temperature (Textreme)risk of hypothermia.

As a general guideline, in the Pyrenees (depending on season and altitude), look for a bag that guarantees comfort on -5 ºC and -10 ºC for winter conditions, or between 0 ºC and +5 ºC for trekking in 3 seasons (spring, summer and autumn). These temperatures can be considered for inside a tent, for winter bivouacs we would go minimum -18ºC of comfort temperature.

Difference between feather and synthetic:

• PenHigher calorific value (fill power usually between 600 and 900 cuin), very light and compressible. However, its effectiveness decreases with humidity.
• SyntheticRetains heat even in humid conditions; tends to be somewhat heavier and bulkier, but less expensive.

3. Add a mat with a good R-Value (or combine them)

The R-Value measures the thermal resistance of the mats. The higher the R-Value, the greater the insulation from the cold of the floor.

• R-Value from 1 to 2Use mainly in summer or in temperate climates (not recommended in high mountains).
• R-Value from 2.5 to 4Suitable for 3 seasons (spring-autumn) with mild nights (down to around 0°C).
• R-Value greater than 4.5Ideal for cold environments and snow; it will even allow you to camp in temperatures of -10 to -15°C, combined with the appropriate sleeping bag.

If you expect freezing temperatures on your journey, you can use two mats (one foam and one inflatable) to enhance insulation..

4. Hot water bottle for heating the bag

A classic and very effective trick in "raw" moments. :

• Use a sturdy bottle (e.g. Nalgene) with 1 L or 1.5 L capacity.
• Fill it with hot water at 60-80°C (not necessarily boiling).
• Place it between the thighs (over the femoral artery) or on the lower back to distribute the heat.
• A well sealed 1 L bottle can keep the heat in for several hours, raising the temperature inside the bag by an additional 5-8°C.

5. Protect your bag and equipment from moisture.

Any humidity drastically reduces the thermal capacity of your bag. To avoid this:

• Use of waterproof covers (with sealed seams) when stored in your rucksack.
• Ventila o dry it in the sun during daytime breaks, weather permitting.
• Put your bag inside a waterproof bag (Dry Bag) if you expect rain or very wet terrain.

6. Consume calories before bed (and in the middle of the night, if necessary).

The body needs fuel (calories) to keep warm:

• A dinner rich in complex carbohydrates (pasta, rice, oatmeal) and some protein ensures sustained energy.
• If you wake up cold, have an emergency snack (chocolate bar or nuts, 200-300 kcal) to kick-start your metabolism.
• Important: avoid drinking too much liquid close to bedtime, so that you don't get up in the middle of the night to urinate, unless you really need to.

7. Don't sleep in wet (or sweaty) clothes.

The water conducts heat 25 times faster than air, so humidity accelerates the loss of body temperature.

• Change into dry clothes before going to bed.
• Always carry a second pair of socks and underwear to sleep in.

8. Use thermal clothing and the layering system for sleeping

• Base layer (first layer): Synthetic material or merino wool (weight 150-200 g/m² for winter mountaineering).
• Intermediate layer (light fleece or primaloft lining): Keeps you warm.
• Outer layer (in case of extreme cold inside the tent): An additional down or synthetic jacket.

It is estimated that the head and neck can account for up to 30% of total body heat loss. A hat o balaclava can make a difference.

9. Ensures good blood circulation

Tight-fitting clothes or compressed socks can hinder blood flow, making your feet and hands feel cold. If you feel pressure, loosen the garment. Keeping circulation active helps to warm up evenly.

10. Use dry twigs and leaves as natural insulation.

If you do not have additional mats:

• Stack leaves, grass or dry twigs under the tent to create an extra layer of insulating air.
• This solution, typical in traditional bivouacs, can lead to a 2-3°C increase in wind chill.

(Who hasn't seen a survival documentary?)

11. Get some exercise before you get in the sack.

• A short (30-60 seconds) session of squats, lunges or push-ups raises body temperature.
• Be careful not to sweat too much; the idea is to enter the bag with your body slightly warm, without soaking your clothes.

12. Fill in the empty spaces in the bag.

• The less air volume is left inside the bag, the less effort is required to heat it.
• Store soft clothing or accessories at the feet or around the torso if the jacket is too big for you.
• Some brands make women's specific jackets (tighter in the foot area and with more insulation in the hips and chest), maximising heat retention.

(Trick: breathe for a while inside the bag).

13. Insulate yourself from direct contact with snow

In winter camping:

• Place a tarpaulin between the base of the tent and the snow, or construct a small wall around the tent to minimise wind entry.
• If camping on snow, use pine branches or blocks of packed snow to create more separation between the tent and the frozen ground.
• Remember that snow is a good insulator if properly compacted, as it traps air.