How to keep warm at night in a bivouac ?

Being cold at night at home is not so bad. We wake up, get up and get an extra blanket. But when it happens to us in a bivouac, it becomes more annoying. In the best case, you just have a horrible night without closing your eyes for a second and in the worst case, it can lead to hypothermia. So to avoid this kind of situation, here are 10 tips to avoid getting cold at night during your bivouac trips:

1. Eat well before going to sleep

Skipping a meal is never a good idea, especially during physical activity. The body needs fuel and eating well is essential, even at night when resting. This is what will allow your body to continue to function normally and in particular to produce heat.

But beware, eating well does not mean gorging yourself! It is estimated that the digestive system accounts for about 10% of your energy over an entire day. Eating too much is too demanding on the body, which would then concentrate on this task instead of warming you up.

Finally, try to eat hot meals as much as possible. The most common choice when hiking is to opt for freeze-dried meals. They are comforting and nutritious after a day of exertion. In addition, the heat from the food can help warm your body.

2. Drink tea and pee!

Hydration goes hand in hand with nutrition. It is just as important. We won’t talk about staying well hydrated during the day, you know the drill. But it is also important before going to sleep. A dehydrated body does not function properly. Again, your body has to compensate and only partially fulfils the function of warming you up.

After your meal, it may also be a good idea to have a hot drink. It can be coffee or tea if caffeine and theine do not keep you awake. Otherwise a herbal tea will do very well. The cup will warm your hands and the drink will warm your body.

As with food, be careful not to drink too much. The risk is that you will then need to urinate during the night. In that case, at the very least, you will have to get out of your sleeping bag if you have the right accessories to relieve yourself in the tent, or else get out of the tent. In both cases, your body will get cold. So it’s a bad idea.

Speaking of needs, it is important not to wait until you feel like urinating. It’s a trick well-known among hikers: go for a pee before sleeping. Otherwise, your body will consume a lot of energy. Energy it won’t use to keep you warm.

3. Warm up with a fire

Lighting a campfire helps to warm the hands and, more generally, the body. It can be useful before going to sleep, while you are cooking. On the other hand, it is not recommended to leave it on while you sleep, unless you are under the stars and there is no risk of a fire starting (in a snowy area for example).

As a little hint, you might think about lighting a fire in a wood stove rather than a campfire. This helps to protect the environment. A fire on the ground kills the fauna and flora below. And that’s without mentioning the ashes once the fire is out or the risk of fire when it is still lit.

This is in keeping with the spirit of Leave No Trace. This educational programme teaches people how to reduce their impact on the environment during their outdoor activities.

4. Insulate yourself from the wind

This is especially applicable if you are sleeping in a hammock or under the stars. It makes sense, but avoid exposing yourself to the wind. For this, you can either opt for a natural shelter with a Robinson Crusoe windscreen with branches and foliage. Otherwise, more trees or a low wall will also do the trick. In the event of bivouacking on snow-capped peaks, the more experienced among you will build an igloo.

Otherwise, there is the tarp. A solution you have to purchase, but which brings a lot of comfort. A tarp is a tarpaulin sheet that provides protection from both rain and wind. If none of these means are suitable, then of course a tent will do. It’s waterproof and it cuts the wind. But you will have to carry it on your back during the day.

5. Have an insulating mattress

The mattress is not only intended to bring you comfort. It also aims to insulate you from the cold. It’s not going to warm you up, let’s be clear. On the other hand, it will keep you from feeling cold. Contrary to popular belief, coolness comes mainly from the ground and not from the air. An inflatable or self-inflating mattress that does not insulate is a sure way to get cold.

To know if a mattress has good thermal resistance, you have to look at the R-Value. This standard is common to all mattresses. The higher this number, the more insulating the mattress. For a bivouac in summer, an R-Value of 1 to 2 is generally sufficient (provided you do not climb too high in altitude). But when entering winter, a mattress with an R-Value greater than 4 is a must if you do not want to be cold while sleeping. If you plan to sleep at high altitudes in the winter, then an R-Value greater than 6 is required. Note that it is possible to stack two mattresses to add up the R-Value. So if you have a foam mattress and an inflatable mattress, this can do the trick.

Extra info: what does the R-Value of a mattress mean?

6. A sleeping bag is imperative

Just as nutrition goes with hydration, so does the mattress with the sleeping bag. A duvet works like this: it traps the heat that your body gives off. This means that rather than being released into the air, it remains contained within your duvet.

To ensure this, the first thing is to choose a sleeping bag in your size. If it’s too small, you won’t fit all the way in and won’t be able to close it. If it is too big, the empty space will be useless and you will need more air to warm up. In order to choose the right sleeping bag size, it is advisable to choose a duvet that is 25 to 30 cm larger than yourself. When you put the hood on, it should be level with your nose.

Then, once the size is correct, make sure you have a comfort temperature similar to what you would have in a bivouac. This data is indicated on the label of the sleeping bags of the main manufacturers (Therm-a-Rest, NEMO, Cumulus, etc.). Do not confuse it with the comfort limit temperature and the extreme temperature, which are irrelevant, since the former means you will still be cold, and the latter means you risk hypothermia and death.

Finally, if you have a duvet sleeping bag (not a synthetic one), make sure you unfold it early enough so that it can take on its fullness. If it is compressed in your bag all day and you take it out two minutes before going to sleep, it will not have time to regain all its properties and you may feel cold for the first few minutes.

7. Have a sack sheet

If, after following all these tips for sleeping without being cold in a bivouac, you are still cold, then you must be one of those people who are always cold! But that doesn’t mean that a winter bivouac trip is out of your reach. There are still a few tips to try out, starting with the sack sheet. It is a light sheet that you put in your sleeping bag. Also known as a ‘meat bag’, it is a compact, lightweight accessory that saves a few precious degrees.

If you want to buy one, be aware that the degree gain given by the manufacturers is usually a little exaggerated. For example, the Sea to Summit Thermolite Reactor Compact Plus Sack Sheet claims a temperature gain of 11°C. In reality, you will gain closer to 7 to 8°C, which remains highly useful in many situations.

8. Don’t put on too many layers of clothing

It’s a bad reflex that we all have: layering up our clothes. Besides the fact that it is uncomfortable to sleep like this, there is a risk of sweating. And perspiration is the enemy of the bivouacker. This is the best way to create the opposite effect and to be cold afterwards.

Therefore, it is advisable to sleep with as few layers as possible. Thermal underwear and a merino wool t-shirt will do the trick. Merino is a soft material, which limits perspiration and regulates temperature. Perfect for sleeping on a trek without feeling cold!

In addition, while it is not recommended to layer up your clothes, do make sure to cover your extremities (head, hands, feet). These are the main entry points for the cold. A hat is therefore mandatory in cold weather. A generous headband can be used as a beanie. And the duvet hood is also a good option. Remember to leave your nose and mouth free. Otherwise, this can create condensation in your sleeping bag which will then lose its insulating properties.

9. The hot water bottle, a classic

There are several ways to create natural hot water bottles. To do so, all you need is to heat water. Then put it in a bottle or reuse an empty freeze-dried bag. All you have to do is slip it into your sleeping bag, in the area of your hands or feet. Once the water has cooled, don’t forget to take it out of your sleeping bag.

Otherwise, there are hand warmers. Easy to use: you light the stick with a lighter. Combustion is slow and this allows you to warm up for many minutes, even several hours for the most elaborate models. We think in particular of the hand warmers from the French brand CAO Outdoor.

10. Exercise before sleeping

Finally, exercising before sleeping is a good way to warm up. We know that it’s not always easy to get motivated after a day of walking. But we’re not talking about doing a marathon here. A few push-ups or sit-ups will suffice. The goal is simply to warm up your body.

Exercising too much will have the opposite effect. You may sweat and make your clothes wet. And then you’re guaranteed to be cold!

As you will have understood, there are many ways to warm up at night while hiking. These tips are well known to lovers of outdoor activities. Remember one thing: it’s all about balance. You have to eat well without devouring everything, do a little exercise without overdoing it, and even cover up without covering yourself too much so as not to sweat. It is with time and practice that you will get to know your body and know how to spend good nights in your bivouac.