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How to Prevent Internal Condensation

I get a lot of questions about tent condensation and how prevent it from forming on the inside of a tent or tarp shelter. Condensation is  a nuisance because it can drip onto your sleeping bag and gear and it makes your tent wet and heavier to carry when you pack it up. It doesn’t matter if you sleep in a “traditional” double walled tent, a single walled ultralight tent, or under a tarp, the causes and cures for condensation are all the same.

Why does internal condensation occur?

The main source of tent condensation is your breath. When you sleep at night, you exhale about 1 liter of water when you exhale. That water vapor is trapped by the outermost wall of your tent or shelter because it has no place to go. If there are 2 people in the tent, then you have to deal with 2 liters of tent condensation, and so on as you add more people.

Storing wet clothes, wet gear, or cooking in a tent can also contribute to internal condensation. So can sleeping near a stream, lake or other wet area when it’s humid and there’s no wind at night.

How can you prevent condensation from occurring?

The best way to prevent the build up of condensation in a tent is to leave your rain fly open at night to promote as much ventilation as possible.  If water vapor can escape out a vent, window or door, you can significantly reduce or eliminate the amount of tent condensation that occurs.

What if it’s raining?

If it’s raining and you are sleeping in a double-walled tent, make sure that the rain fly is stretched as far away from the inner tent as possible, particularly along the sides and corners of the tent. If your fly clips onto the base of your inner tent, consider staking it out separately to promote more airflow between the layers.

Another thing you can try is to unzip or clip the rain fly half way up so that you get more ventilation. The same holds for a tent vestibule. Here’s an example of what I’m getting at (above). Shown here is the front vestibule of a single walled Tarptent called the Squall 2, but you could rig something like it up with the rain fly of a double-walled tent. I’ve slept through incredible rain storms in this tent and never had rain blow inside, but depending on the shape of your tent and its fly, you’ll need to find the perfect balance between rain cover and ventilation.

Well Ventilated Vestibule of a Tarptent Squall 2
Well Ventilated Vestibule of a Tarptent Squall 2

How can you reduce the weight of a wet tent or tarp?

If you’re not in a rush, you can let it dry in the morning sun, but that might take a while. If you have to get going, another option is to wipe down the rain fly using a clean camping towel, which will remove a significant amount of that water. After that pack the fly away in an outer pack pocket or in a separate plastic bag to keep it from making your other gear wet.

Can you set up a wet rain fly at night?

Absolutely, although you might want to pitch camp a little early that evening so that your tent has a chance to dry out before you want to get into it. I’ve set up damp tents in summer and had them dry within an hour, but your mileage may vary.

Do you have any other internal condensation tips?

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12 comments

  1. Nice article about condensation. Ventilation is the key for condansation. Also the campsite is important. If you’re near a river or lake prefer a higher place. Even 10-20 meters up make difference.
    Always check the wind direction and weather report. Place the tent according to the wind to have better ventilation.
    I have tarptent rainbow and have some condansation in really humid areas. Mostly when there’s no wind. A small towel does the job. Some drops of water is nothing to worry about.

  2. I found some years back that a mylar reflective tarp over the top of the tent (it make take two or three, depending upon tent size), prevented condensation where it covered the tent. Areas that were not covered, such as an edge, had normal condensation.

    First time I used it was in Oregon’s coast range. High humidity. I put the tarp over the pup tent, but there were about 3″ near the entrance that it didn’t cover. Everywhere the tarp covered was completely dry in the morning. The areas not covered were damp inside. It also made for comfort as I slept on top of my mat and blanket, rather than having to use them, despite the ~50 degree morning.

    Since then I’ve used reflective tarps over tents and there’s no comparison as far as comfort level.

  3. Just used a tarptent cloudburst 2 for the first time and I set it up in the early evening and by bedtime there were droplets of water all over the inner before I even got in. Lovely to use and set up but not impressed so far with condensation.

    • Mark,
      Yes, single walled shelters will build up condensation faster than double walled ones. Well, not technically true. Condensation will usually happen on the surface with the greatest temperature differential. If you have a single walled shelter, all (or most) of the condensation will collect on that single skin. With a net tent inner, the same thing happens, but, you usually don’t notice it as much because the inner net protects you from rubbing against it. This makes a case for a two layer insulated tent, such as one made from insulated building material. It will perform better because there is a lower temperature differential between the surfaces. Setting up in wet ground will make things much worse because you get water vapor from the ground as well as from you. At 60F and 50% humidity it will not be too bad. At 40F and 100% humidity you WILL get a lot. Conditions, ventilation, size, number of occupants, and mode of setting it up all have rather drastic effects on the amount of condensation.

  4. Hopefully it is the weather as last night (I am on a trip now) I had to wipe the inner twice and that cond’n just keeps on comin’. Going to try and re set it after it has dried and later in the evening once it is cooler.

  5. Backpack in the rain, problem solved, :) Guys, no way to stop condensation in in climatic weather conditions, live w it and take a pack towel along for the ride. most of all, have fun and remember, this is very important. The minute you stop letting condensation ruin your trip the sooner it will stop i promise!

    • Love your thinking. As they say, life is 10% what happens and 90% how you react to it.

      Every day I’ve backpacked in the rain was better than being in the office on a sunny day.

  6. Yeah, condensation is a pain. There are a couple things you didn't mention, but, given the brevity of the article, that's OK. Evaporative cooling can intensify condensation. This is where the water from condensation begins to evaporate, further cooling the surface of a tent and causing *more* condensation. "Like begets like" as the saying goes… Also, the material of the tent itself. A highly breathable material, like Epic or even Gortex, will allow moisture vapoure to escape, but will not allow water to penetrate. But, this is expensive. This is a huge drawback to cuben. Silnylon (a common tarp material) breaths slightly, not enough to do any good, though.

    The main problem in three season tents is lack of temperture regulation along with the moisture. It is the difference between the two areas separated by a fairly impermiable film (the tent skin) that causes condensation. The ventilation scheme for most UL tents and tarps is ignored. You need a low inlet and a high outlet, given still conditions. The vents should be about the same size and large enough to ventilate your breath and any escaped body heat. One thing that can help is to have a high vent (about 8-10" diameter or ~39.5 to ~50.0 sqin) and hang a candle (say a UCO candle lantern) about 6-8" below the vent. This will "drive" the ventilation using the fact that "Heat rises" and moist air is lighter than dry air. Of course, you will *still* get some condensation…in some conditions it will happen. No tent manufacturors I know of bother with large top vents, unfortunatly. It is fairly easy to modify your tarp or tent, though. Even the Stephensons designed tents have too small a top vent.

    Larger volume works well to mitigate much of the temp/moisture difference. A two man tent with a single ocupant will not produce as much moisture, as you say. Not as warm in winter, also not as condensation prone. In winter it is easier to shake off most ice dropplets or condensation, anyway. And the air is usually much dryer, to start with. But for those bad temps (between 25F and 40F) a larger tent/tarp can help. But, you pay the weight penalty.

  7. "Clean camping towel"? That must be American for "your mate's sock"…

    Pitching your tent so the vents align with the prevailing wind also makes a heck of a difference.

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