Why is the inside of my tent wet in the morning?

Telling condensation from a leak, why ventilation matters more in cold weather, and the pitching choices that make it worse.

Difficulty: beginner
Time: 20 min
Read: 3 min

Short answer

It is almost always condensation rather than a leak. You breathe out around a litre of water overnight, and in a sealed tent it condenses on the cold flysheet. Open every vent, keep the inner off the fly, and pitch away from damp low ground.

New campers usually assume a wet tent interior means a leaking tent. In a modern tent it is nearly always the water you exhaled, condensing on a cold surface a few centimetres from your face.

Step by step

Work out whether it is a leak or condensation.Condensation is an even film of droplets on the inside of the flysheet, worst at the top and on the coldest side. A leak is localised, usually at a seam, a zip or a peg point, and appears during rain rather than overnight.
Ventilate, even when it is cold.Open all the vents and leave a door partly unzipped. This feels wrong on a cold night and it is the single most effective fix — moist air has to be able to leave.
Create a through-draught.Vents at both ends, or a vent low on the windward side and one high on the leeward side. Air needs to enter and leave, not just have one opening.
Keep the inner tent off the flysheet.Peg the fly out taut so the two layers do not touch. Where they touch, condensation on the fly transfers straight through to the inner and drips on you.
Pitch on higher, drier ground.Cold damp air pools in hollows and beside water. A slightly raised, open pitch has noticeably less condensation than a sheltered dip by a stream.
Keep wet things out of the inner.Boots, waterproofs and wet dogs go in the porch. Anything wet inside evaporates overnight and condenses on the fly.
Do not cook in the tent.Aside from the serious carbon monoxide risk, boiling water releases a large amount of moisture into a small space.
Expect more condensation in certain conditions.Cold clear nights, high humidity, still air and a full tent all increase it. A single-skin or very cheap tent will always condense more.
Wipe it down in the morning.A small cloth or a chamois takes the film off in a minute and keeps the inner and your kit dry as you pack.
Dry the tent properly at home.Never store a tent damp — mildew develops within days and permanently damages the coatings and the smell. Pitch it in a garden or hang it indoors until completely dry.
Reproof if water is genuinely getting through.If it really is a leak, seam sealer for seams and a proofing spray for a flysheet that has stopped beading. Test with a hose before the next trip.

Tips

Ventilation, not insulation. A sealed tent is a wet tent.
Wherever the inner touches the fly, you will get drips. Pitch the fly taut.
Never store a tent damp. Mildew is permanent.

Common mistakes

Closing everything up to stay warm — Each person exhales roughly a litre of water vapour overnight. With nowhere to go it condenses on the flysheet, soaks bedding and makes the tent much colder, not warmer.
Pitching in a sheltered hollow — Cold, moist air sinks and collects in dips, so a hollow that looks nicely sheltered is both colder and far damper than slightly higher open ground.

If it doesn't work

Even film of water inside the flysheet

Cause: Condensation — Fix: Open all vents and a door, pitch on drier ground, and keep wet gear in the porch.

Drips onto the inner tent

Cause: Inner touching the fly — Fix: Re-peg the fly taut so the layers are separated all round.

Water at seams during rain

Cause: Failed seam tape — Fix: Apply seam sealer to the inside of the affected seams and let it cure fully.

Water pooling under the groundsheet

Cause: Pitch in a hollow or on saturated ground — Fix: Move to higher ground; never dig a trench around a tent on managed land.

Musty smell

Cause: Packed away damp — Fix: Pitch and dry it fully, clean with a tent-specific cleaner, and never store it wet.

Questions people ask

Is a wet tent inside always condensation?

Not always, but usually. Condensation is an even film across the fly, worst at the top; a leak is localised and appears during rain. A tent that beads water on the outside but is wet inside is condensing.

Do single-skin tents condense more?

Considerably. Without a separate inner there is nothing between you and the cold outer surface, so anything that condenses lands directly on you and your kit.