Why Is My Sleeping Bag Wet?

A sleeping bag is one of the best inventions for tent camping. They are efficient, warm, and compact. It is imperative though to make sure that your sleeping bag stays dry. This is particularly the case when it comes to maintaining your down sleeping bags insulating qualities since a very wet down bag will not insulate you from the cold. You may be camping though and wake up with a wet sleeping bag. This is concerning particularly if you are traveling or the conditions do not allow you to sufficiently dry your bag out during the day.

Why is my sleeping bag wet? Your sleeping bag is wet because your body gives of moisture inside of your bag while you sleep. If the dew point is inside the layers of your bag moisture will get trapped in your bag and not escape. If the dew point is outside your bag moisture can settle on the exterior of your bag. If you are sleeping in sub zero temperatures the surface of your bag can frost over. It is important to keep your tent well ventilated, not to go to sleep with damp clothing on, to breath outside of of your bag, and in sub zero temperatures make sure your neither too hot nor too cold inside your bag. Placing a wool or synthetic blanket over your bag in sub zero temperatures will help eliminate frosting on your bags surface.

Cold Weather Camping Condensation

If you are camping in sub zero temperatures you can easily get frosting on the surface of your sleeping bag. This is not so much of a problem if you are base camping since you can allow your bag to dry sufficiently each day. If you have access to a wood stove or other heat source than this can help you dry your bag out even more during the day.

The problem comes when you are traveling each day and need to pack away your sleeping bag. Instead of evaporating away, packing up your bag can cause the surface frost to melt and soak into your bag. Over the course of a trek your bag can collect a lot of moisture this way. If your bag is good quality whether down or synthetic and keeps you nice and warm at night, the heat from your body while you are asleep will help push this moisture out.

If you are sleeping too hot or too cold than this can be a problem in winter camping. Too hot and you will be sweating at night and only exacerbate the moisture problem, too cold and you may not be sufficiently pushing the moisture out of your bag. This puts your bag at risk of having a dew point within your bags layers. Rather than only frosting on the bags surface, air will be condensing inside of your bag.

Another way to minimize condensation in or on top of your bag is not to go to sleep with damp clothing. You may feel like the clothing you wore during the day is sufficiently dry, however there can still be quite a bit of moisture in your clothes from exertion and sweat during the day. This moisture will only add to your condensation issues. Go to sleep with a change of dry clothes, none at all or with only dry thermals.

It is also important to make sure that your tent has good ventilation. You may need to keep damp clothes or things inside your tent (probably better in a vestibule), and all the humidity inside your tent needs to be able to escape easily. If you are camping in a canvas tent than you are already in one of the best ventilated tents around since canvas is a natural fiber and breathes. However, even in a canvas tent you can get frosting on your sleeping bag in sub zero temperatures.

Another way to minimize frosting or icing on your bag in sub zero temperatures is to place a wool or synthetic blanket over the top of your bag. Wool is the best choice since it breathes extremely well. You don’t even need to use a full length wool blanket since most of the frost will accumulate around your upper body and head area. Breathing outside your bag will also help minimize frosting around your head. The wool blanket not only protects your bag against frost but also absorbs any moisture that may otherwise collect on your bag and freeze. Wool will be easier to dry than a large down bag and it will still insulate even when damp.

In very cold temperatures in excess of -20C/-4F and if you will be needing to pack up your equipment everyday it may be advantageous to consider purchasing A VBL (vapor barrier liner). These are a completely waterproof liner that goes over your thermal clothing inside your sleeping bag. A VBL prevents moisture from entering your sleeping bag from your body eliminating any icing on your bag. VBL’s are not incredibly popular due to the image in peoples minds of sleeping in their own sweat, and the resulting feeling of being clammy, however VBL’s will get the job done and if worn above your thermals will minimize the clamminess. You will be able to pack up your sleeping bag every day and not need to fear a buildup of moisture inside your bag.

Condensation Under Bag

Another problem is condensation under you sleeping bag. It is important to use a thermal air mattress for sleeping. If you sleep directly on the ground not only is the ground colder but it can also be damp. This dampness can get into your bag. Even if you are sleeping on the floor of your tent, moisture can leave you body and get trapped between the moisture resistant floor and your sleeping bag making you feel clammy. Sleeping directly on a hammock or cot can also cause condensation problems. Not only is it cold (part of the problem) since a compressed bag has no loft but the dew point can be below you as well as above. A ground mat, thermal mattress or other buffer that adds loft below you will not only insulate you, it will also protect your bag from condensation and provide a dryer sleeping experience.

Some experience condensation between their sleeping bag and their thermal mat. There could be various reasons for this however one solution would be to make sure your thermal mat is sufficiently inflated to allow more air flow. More air flow will allow more moisture from your body to escaped out from under your bag.

Sleeping Outside Your Tent

Out In The Open (“Cowboy Camping”)

Some would like the experience of sleeping outside in the open air. Just their sleeping bag, mattress and the stars. Some very much enjoy this experience, however there is the challenge of morning dew making you wet. Some ways to mediate this problem would be to consider the air humidity level that evening before you go to sleep. If the air humidity is high either from the weather or the location you are in than you increase the risk of condensation. If the night will be clear its better to try to sleep under some trees, this will minimize being wet from dew in the morning. Putting down a ground sheet can also help you be less effected by ground dampness.

Sleeping Under A Tarp

Sleeping under a tarp is another popular way to camp. Condensation is always higher though in single walled tents and shelters since there is no buffer between you and the condensation. In most cases if you don’t come in contact with the tarp fabric and the condensation runs down the walls to the ground rather than on you then you won’t get wet. Making sure there is good air circulation under the tarp can help reduce condensation. Also avoid camping in low lying areas that are damp, such as near rivers, streams and lakes and in open grassy fields. Try to limit the amount of people sleeping under your shelter which will also cut down on the condensation.

Bivy Shelter

A bivy is a portable shelter that originally was designed so that emergency climbers and mountaineers could take shelter from weather where a larger shelter would be impractical. Bivy’s are very similar to each other in function with only slight differences and they are made out of various materials. Some are more breathable than others and offer protection from rain. Bivy’s can struggle with condensation issues since they are mostly single walled and they allow very little to no space between it and your sleeping bag. However, they have the advantage of being extremely compact and can be set up in no time.

Tent Leakage

The final reason that people get a wet sleeping bag is that their tent or shelter is actually leaking water. Sometimes in a rainstorm your tent may appear dry at first but over time weaknesses begin to show up. Rain water can begin to make its way through poorly taped or sealed seams and floors. A very low HH (hydrostatic head) rating on a tent can also be why your tent is leaking. Tents that have a low HH rating begin to “wet out” in heavy rain allowing moisture and rainwater to enter your tent.

Poor Tent Ventilation

Finally, poor tent ventilation is another factor why your bag is wet. It is important to purchase a tent that has good ventilation so moisture building up inside your tent can escape. Remember to open all your vents and windows. This is particularly important if your tent is single walled.

Conclusion

Waking up at night or in the morning with a wet or damp sleeping bag is not a happy experience. Moisture buildup inside your sleeping bag can become life threatening in extreme cases and situations so it is important to understand what the contributing factors are and what you can do to avoid them as best as you can. At the very least being able to enjoy a dry sleeping experience will go a long way to enjoying your tent camping experience. You, your family and friends will be able to look forward to your next camping experience rather than being overly concerned about whether or not your bag will feel dry.