Condensation in Tents: Why You Wake Up Wet and How to Stop It

Tent condensation is not a leak, and it is not a defective tent. It is the half-litre of water you breathe and sweat out every night, plus whatever your wet gear and the ground add, hitting a wall that is colder than the air inside. Understand where the water comes from and where it goes and you can cut it to a few drops, choose a shelter fabric that lets it out, and sleep in a bag that does not care about what is left.

Where the water comes from

An adult loses roughly 0.5 litres of water overnight through breath and skin, more after a hard day or a big dinner, and that figure is per person. Two people in a small tent produce about a litre of vapour between dusk and dawn. To that add:

• Wet gear. A rain jacket, socks and a pack brought inside can hold another half-litre, all of which evaporates into the tent air as it warms.
• The ground. Damp soil under a floor, or bare ground under a floorless shelter, gives up water all night. A meadow at dusk is a humidifier.
• Cooking. Boiling a litre for dinner in the vestibule puts a large share of it into the air as steam.
• The outside air itself. On a still, clear night near water, relative humidity outside can reach 100 percent. Then the tent is not the problem; everything outside is wet too.

Dew point and the cold inner wall

Warm air holds more water vapour than cold air. The temperature at which a given parcel of air is saturated and starts to shed liquid is its dew point. Inside a tent the air is warmer and wetter than outside, so its dew point is high. The tent wall, meanwhile, is cooled from the outside by the night air and, on a clear night, by radiating its heat to the sky; a fly can be colder than the air around it. When inside air touches a wall that is below its dew point, water condenses on the fabric. It beads, runs to the low points and drips onto whatever is beneath: usually the foot of your bag.

Three things follow. The bigger the gap between inside and outside temperature, the worse it gets, which is why cold, clear autumn nights are the worst and mild overcast ones are fine. The less air exchange, the worse it gets, because vapour accumulates. And any surface colder than the inside air will collect water, which includes a single-wall tent, the underside of a low tarp, and the outside of a sleeping bag lying against the wall.

Why coated nylon single walls are worst

A waterproof nylon tent is waterproof because of a polyurethane or silicone film on the fabric. That film is a vapour barrier: what keeps rain out keeps your breath in. In a single-wall coated tent every drop you exhale either leaves through a vent or lands on the wall, and the wall is the coldest surface in the room. Silnylon and similar fabrics also sag when wet, bringing the cold wet wall closer to you.

A double-wall tent does not stop condensation; it moves it. Vapour passes through the mesh or uncoated inner, condenses on the underside of the fly, and the inner keeps you from touching it. In heavy conditions the fly still drips through the mesh and the inner wall wets from the outside. It is better, not solved, and it costs the weight of a second layer.

How to stop condensation in a tent: ventilation rules

You cannot stop producing vapour, so the job is to move it out faster than it collects. Air exchange beats everything else on this list.

1. Cross-ventilate. Open a vent or door at each end, low on the windward side and high on the lee side, so air enters, picks up moisture and leaves. One opening does little; two make a draught.
2. Leave the door cracked. Even a hand’s width unzipped at the top of a door halves the problem in most tents. The cold you feel is less than the cold of a wet bag at 5 a.m.
3. Pitch the fly high. Stake the fly out and off the ground so air moves under the edge. A fly pegged to the dirt is a bag around a bag.
4. Do not cook inside. Steam is the fastest way to soak a tent, and stoves in tents are a carbon monoxide risk on top of that. Cook under a tarp or in the open.
5. Keep wet gear out. Wet jackets and packs live under the vestibule or the tarp, not in the sleeping space.
6. Breathe out of the bag. Cinching a hood over your mouth puts half a litre of water straight into the insulation. Keep your nose and mouth outside the bag and wear a hat instead.
7. Keep the bag off the walls. Choose a tent long enough that the foot does not press the fabric, or angle it across the floor.
8. Wipe in the morning. A small cloth on the inside of the fly before you take it down means you pack a damp tent, not a wet one.

Site choice

Half of tent condensation is decided before the first stake goes in. Cold air is heavy and drains downhill at night, pooling in valley bottoms, hollows and the low side of meadows, and it arrives saturated. Lakeshores, riverbanks and marsh edges add water vapour to the pool. Open ground under a clear sky radiates heat upward all night and gets coldest of all.

• Camp on a slight rise, a bench or a shoulder, 20 to 50 feet above the valley floor if you can, where cold air drains past you rather than into you.
• Stay back from open water and wet meadows; 200 feet is a good rule for other reasons too.
• Pitch under a tree canopy on clear nights. Trees radiate warmth back down, so the tent surface stays a few degrees warmer and closer to the dew point of the air rather than below it. Watch for dead limbs overhead.
• Put the door across a light breeze rather than blocking it. A little moving air is the whole point.
• Dry ground beats lush grass. Pine duff and bare mineral soil give up far less water than a meadow.

How breathable canvas changes the equation

Everything above assumes the wall is a barrier. A cotton canvas wall is not. Cotton fibre absorbs 7 to 8 percent of its weight in water vapour at 65 percent humidity (published textile data), and a woven, uncoated canvas passes vapour through the fibre and the weave rather than stopping it at a film. Beeswax-sealed canvas sheds rain by surface repellency and by the fibres swelling to close the weave, while the wall continues to breathe. The result is that a canvas tipi in the same cold, clear conditions that leave a nylon tent dripping stays dry inside, with the night’s moisture dispersed through the fabric. Lucky Sheep’s organic canvas tipi has no polyurethane coating, no PFAS and no flame retardant; the only thing between you and the sky is cotton and beeswax.

Canvas is not magic. In prolonged heavy rain the wall darkens and water runs down its inside face; touch it and you start a drip at that spot. It is heavier than nylon by a wide margin, about 10 lb of canvas for the 9-foot tipi, so it is a basecamp shelter, not a backpacking one. And a wet canvas tent still has to be dried before storage (see canvas tent care). But for the specific problem of waking up wet from your own breath, breathable fabric solves what ventilation only manages.

Why a wool bag tolerates what still lands on it

Some moisture reaches the sleeping bag no matter what: a drip from the fly, dew under a tarp, fog, and the vapour your own body pushes out through the insulation all night. What happens next depends entirely on the fill.

Down clumps as it wets and loses loft, and loft is all the warmth it has. Polyester fill absorbs almost nothing, about 0.4 percent of its weight, so the water sits as liquid on the fibre surface and against the shell, which is the cold, clammy feel of a damp synthetic bag. Wool absorbs 13 to 16 percent of its weight in vapour before it feels damp, holding the water inside the fibre where it does not displace the trapped air, and it releases heat as it does so, roughly 960 kJ per kilogram of water absorbed (see heat of sorption). A wool bag on a damp night gets slightly warmer as it takes on moisture and then dries from the inside out the next morning in the sun.

The Rewilder is built for exactly that night: 2 or 3 inches of US wool batting under a beeswax-treated organic cotton shell that sheds the drips, with a merino or WeatherWool liner against the skin. It is field-rated to 20°F in the 2-inch loft and 10°F in the 3-inch; those are field ratings, not ISO 23537-1 lab tests. It weighs 4 lb in the Standard 2-inch, about three times a 20°F down quilt, and it will still be warm at 5 a.m. when the fly is dripping. The wool sleeping pad underneath does the same job against ground moisture, with no foam to trap water and no air chamber to chill.

The short version

• You make about half a litre of water a night. It has to go somewhere.
• Camp high, dry and under trees; keep wet gear and stoves out; open two vents.
• Coated nylon traps it; double walls hide it; breathable canvas lets it out.
• Whatever lands on the bag, wool absorbs it and stays warm. Down and polyester do not.

Reviewed August 2026. Moisture-regain and heat-of-sorption figures from published textile data; overnight water loss is a typical adult figure and varies with exertion, altitude and temperature.