Whether you are in a static camp or making a journey, looking after your sleeping kit is a priority.
Moisture retained in your sleeping bag will significantly reduce its thermal efficiency. A damp bivvy bag will increase heat loss by evaporation.
Moisture From Within
We all give off moisture while we sleep. If we are too warm we sweat. This is obvious and can largely be prevented by removing layers of clothing, unzipping sleeping bags, opening bivvy bags and generally increasing ventilation.
Even if we are not sweating, however, we are giving off moisture all the time. Imperceptible perspiration helps keep our skin from becoming too dry. It also means that, during sleep, we can lose around a third of a litre of moisture into our sleeping bag without even realising.
Moisture From Without
Air at night is typically cooler than during the day. Cooler air has a lower capacity to retain moisture, which translates to cool, damp air and the formation of dew.
Dew is a form of condensation and it tends to increase as the air temperature drops.
Condensation of moisture from inside your sleeping equipment also tends to increase as the temperature drops. The main reasons for this are that, first, the cooler air outside is more likely to be saturated and therefore evaporation of the moisture from your perspiration is harder to achieve; second, as the external temperature of your sleeping equipment decreases, water vapour is more likely to condense on the inner surfaces.
In extremely low temperatures (around minus 20 Celsius and below), condensation can actually just freeze on the inside.
The ground is often damp. Laying on the ground will make whatever is between you and the ground damp too. Lying on frozen ground or snow also has the potential to introduce moisture to your sleeping equipment.
An obvious potential source of moisture on the outside of your sleep system is rain. Even if the outer cover of your sleeping kit is waterproof, it just being wet will increase evaporative heat loss. This may be unavoidable while it is raining but make sure you get it dried off as soon as you can.
As air temperatures drop below freezing in the winter months, or at higher altitudes, frost can form overnight (where condensation would form at higher temperatures). Again this can be from moisture in the air (forming on the outside) or perspiration forming on the inside of sleeping equipment.
All the moisture we have discussed so far has either been due to perspiration or the environmental conditions. Your breath contains a lot of moisture (you can see this on a cold day). If you breathe into your sleeping bag at night, then you add much more moisture to it than you do if you breathe outside of it.
On chilly evenings this extra moisture may cause you to be cold during the night. It can also be difficult to get rid of unless you have the right conditions the next day.
In consistently sub-zero (Celsius) temperatures, breathing into your sleeping bag can cause serious problems, with the build up of frost within your sleeping bag impossible to remove unless you enter a warm, dry environment such as a cabin or heated tent. Breathing moisture into your sleeping bag in an Arctic environment will literally render your sleeping bag unusable in a relatively short period of time.
Get Some Air
Under most conditions, the primary way you should remove moisture from your sleeping equipment is to air it out.
Get your sleeping bag airing as soon as you get up. The bag will still be warm and this warmth can mobilise moisture to evaporate.
Open your bag out to maximise the effect.
Get Some Sun
A light breeze of relatively dry air will do a good job of removing moisture from your sleeping kit. If you can get the sun on your sleeping equipment – particularly your sleeping bag – all the better.
Air All of Your Kit
While your sleeping bag is most affected by moisture, all your other sleeping kit contributes to keeping warm and should be kept as dry as possible.
What If It’s Raining?
If it is raining or your are concerned about the possibility of rain, then you can hang your sleeping bag under a tarp using a hanging line.
If conditions are particularly humid then there may be no immediate benefit to airing your sleeping bag at all. In this case, leave it in your bivvy bag, or tent, until the opportunity to air it arises.
Some Extra Considerations For Your Sleeping Kit
If you have placed all your sleeping kit inside a bivvy bag, then the bivvy bag will have been in contact with the ground. This can leave the bag really quite damp and it may need airing/drying for longer than either your sleeping bag or sleeping mat.
Condensation can form on the underside of your sleeping mat too, so make sure you air this off so it is packed away dry, ready for the next evening.
In sub-zero temperatures, water vapour may well have frozen on the interior of your bivvy bag. Below around minus 20 degrees Celsius, this happens even with ‘breathable’ bivvy bags. Simply turn the bag inside-out and shake off the frost.
A Little Effort Pays Dividends
Paying attention to the care of your sleeping kit will maximise its effectiveness in its intended purpose, i.e. keeping you warm for a comfortable night’s sleep. Tiredness, irritability and easy fatigue are all effects of poor sleep. Taking a few minutes in the morning to take advantage of any sun or breeze to air out your sleeping kit will always pay dividends.
On a wilderness trip or expedition good rest is much more important than on a leisurely camping weekend. But you’ll also be more likely to need to pack up and move on each day in order to reach your destination. Even 15 minutes of airing while you make a brew and eat your breakfast can make a significant difference to the condition of your sleeping kit.
What Do You Do?
What other tips do you have for keeping your sleeping kit in top condition? Let us know in the comments below…
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