Why Tents Get Wet Inside: Condensation and Ventilation
Waking to damp walls and a dripping ceiling does not always mean the tent leaks. People breathe out a surprising amount of moisture overnight, and when the tent fabric is colder than the air inside, that moisture condenses on it. Managing condensation is about airflow and location.
When condensation is worst
Clear, calm, cool nights near water or in damp hollows produce the most condensation. Cold air settles in low spots, and humid air near lakes and streams adds moisture. Wet gear stored inside the tent makes it worse.
Single-wall tents tend to show it more than double-wall tents, where the inner mesh keeps you away from the wet fly.
Ventilation helps most
Open the fly vents and, if weather allows, keep a door partly unzipped so moist air can escape. Pitch the fly taut and away from the inner tent so air can move between the layers.
A slight breeze is your friend. A site with a little air movement often stays drier than a perfectly sheltered one.
Living with it
Keep sleeping bags away from the walls and wipe the ceiling with a small cloth in the morning. Shake off and dry the fly in the sun before packing, or dry it at the next stop.
Never cook or run a heater inside the tent to dry it; fuel-burning appliances create carbon monoxide in an enclosed space.