How to stop waking up wet: tent condensation, explained

Why it happens at all

Every sleeping adult exhales roughly a pint of water overnight. Warm damp air hits the coldest surface it can find and condenses there. The colder and stiller the night, the more of it there is — clear, calm, cold nights are the worst, not rainy windy ones.

Wet ground makes it much worse. A tent pitched on a river bar or damp grass is sitting on an evaporating surface all night, which is why the same shelter can be dry on a ridge and dripping in a meadow four hundred feet below.

What actually helps

Site choice does more than any feature. Higher, drier, with a little moving air. Cold air pools at the bottom of valleys and beside water; that is where you will be wettest.

Ventilation second. Peak vents, a cracked door, a fly pitched an inch higher off the ground — anything that lets the damp air out beats anything that tries to keep it in. In rain that feels wrong, and it is still correct.

Wall type third. A double-wall tent does not produce less condensation, it just collects it on the fly where it cannot soak your bag. If you sleep cold and hate wiping down a wall in the morning, that is worth ten to fifteen ounces.

What does not help

Paying more. A $795 Dyneema single-wall shelter condenses about as readily as a $260 silpoly one; the vents in the expensive ones reduce it, they do not remove it. Anybody who tells you their single-wall tent never condenses has been lucky with the weather.

A small towel or a bandana is 0.4 ounces and solves the practical problem completely.