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 Squall2, 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.
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.