Dealing with Condensation in a Bivy Sack

If you’ve spent any amount of time in a bivy sack that wasn’t particularly breathable, then you know all too well how uncomfortable and irritating condensation inside the sack can get. A lot of us spend way too long just assuming that this is one of the unavoidable aspects of a backpacking life.

Let go of this idea and keep reading to learn how dealing with condensation in a bivy sack is easier than you might think.

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What Causes Condensation in a Bivy?

Cold Weather and the Dew Point

Cold nights are typically what bring about our dreaded condensation problems. In cold climates, or in areas where the temperatures drastically drop at nighttime, it is common for the dew point and temperature to reach the same level while you’re trying to sleep. To learn more about dew points, check out this Live Science article on the subject.

When this happens, moisture can begin to easily collect along cool surfaces, including your bivy sack. Moisture will begin to line the inside of the bivy, and before long enough will have accumulated to cause uncomfortable dampness. As this cools, your bivy can begin to lose its warmth, comfort, and effectiveness.

Exhaling into Your Bivy Sack

One of the biggest causes of this condensation comes from your own breath. As you exhale into your bivy sack, the air you breathe out is significantly warmer than the bivy material which is being cooled by the cold night air. Moisture from your breath will begin to collect inside your bivy sack throughout the night.

Sweating Through the Night

Additionally, your body’s fluctuating temperature can cause the same issues. Even though you may enter your bivy cold, throughout the night your body will naturally heat up and begin to sweat. This moisture, like your breath, can begin to condensate in the bivy sack as well. In some cases, this won’t be too noticeable or uncomfortable to begin with but will gradually increase the dampness and weight of your bivy over time.


It is far less common for these issues to arise in significantly warmer environments unless those environments are particularly humid. If the material of your bivy is warm rather than cool, then it won’t collect condensation. However, the natural moisture in the air when it’s humid could present similar problems.

How to Reduce Condensation in a Bivy Sack?

Breath Outside of Your Bivy Sack

To reduce condensation in a bivy sack you have to reduce the amount of moisture that gets released into the bivy in the first place.

One way of doing this is to avoid exhaling into your bivy. Sleeping with your head outside of the bivy is the most obvious way of doing this, but sometimes extremely cold temperatures don’t allow for this. In situations like this, simply unzipping one small hole in the bivy can do wonders. It allows the moisture from your breath to escape the bivy entirely, rather than collect inside.

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Wear Fewer Layers at Night

Secondly, you can wear fewer layers when you go to sleep at night. While we often layer up to stay warm, this can actually be counterproductive. Too many layers will increase your likelihood of sweating, which is allowed to collect in the form of condensation can lower the temperature of your bivy. Instead, opt for one warm layer of thermals at night.

Let Your Bivy Sack Breath

Over time, condensation can make your bivy heavy, damp, cold, and uncomfortable. This only worsens the longer you let moisture accumulate. A great tip for preventing these things is to regularly air out your bivy sack. We recommend unzipping and hanging your bivy up each morning to let it breathe.

Additionally, choosing a bivy sack that is constructed with breathable and well-ventilated materials before you even leave for your adventure can go a long way in preventing condensation. Check out Outdoor Gear Lab’s bivy recommendations for some high-quality options.


We hope you’ve learned some useful information on how to keep your bivy dry, warm, and comfortable all through the night. Say goodbye to condensation by reducing the moisture in your bivy sack and always be sure to air it out in the morning!

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