Why does my tent drip on the inside?

A tent that drips on the inside is nearly always condensing, not leaking — and the difference is visible if you look at the pattern rather than the puddle. Every person in a tent puts out moisture through the night, and so does the ground beneath it. That moisture has to go somewhere.

Telling the two apart

Condensation appears as fine droplets spread evenly across a whole panel, heaviest on the coldest surface — usually the inside of the flysheet near the apex, and the underside of any single-skin fabric. It is worst on still, clear, cold nights, and it wipes off leaving a dry surface behind.

A leak is local. A wet line following a stitched seam means the factory seam tape has lifted. A patch spreading from one point means damage or coating failure at that point. Water appearing at the base of a wall, on the other hand, may not be either — it may be water running along the ground and under the floor.

Establishing which you have is the whole diagnosis, because the fixes have nothing in common.

Where the moisture comes from

Two sources, both unavoidable. People produce water vapour continuously through breathing and through skin. And the ground gives off moisture, especially damp turf, which is why a pitch on grass condenses more than one on gravel or rock.

Add a night with no wind and a clear sky, when the fly radiates heat away and its surface drops below the dew point of the air inside, and every gram of that vapour finds the coldest thing available.

Cooking inside a porch adds a great deal more, and the stove maker’s instructions govern whether that is permitted at all with your stove.

Reducing it

You cannot stop condensation. You can move most of it somewhere harmless.

Ventilate, even when it seems wrong. Vents at both ends produce a through-flow that carries vapour out; a tent sealed against the cold traps it. Most tents have adjustable vents at the apex or over the doors, and they are the first thing to open.

Pitch where air moves. A hollow or a dense thicket is still, and still air is where the worst condensation happens. A slight rise with some airflow is drier than a sheltered dip.

Keep the inner off the fly. A double-skin tent works by condensing on the fly and keeping the inner clear of it. Anywhere the two touch, moisture transfers straight through — which is what most people are actually seeing when they report a drip. Retensioning the guylines usually fixes it, and on siliconised nylon that means retensioning after rain, because the fabric stretches when wet.

Keep wet kit outside the inner. Wet clothing hung inside evaporates into the same volume of air all night.

The morning routine

Wipe the inside of the fly down with a cloth or a small pack towel before packing. It takes a minute and it is the difference between a dry tent going into the bag and a wet one.

Where the weather allows, shake the fly out and let it dry before it is stuffed. A fly packed damp for several days grows mould that stains permanently and attacks coatings, and that is a real fault as opposed to a nightly nuisance.

If it really is a leak

Look at seams first. Lifted seam tape is far commoner than fabric failure, and it is treated with a seam sealant matched to the fly’s coating — silicone-coated and polyurethane-coated fabrics take different products and are not interchangeable, so read the fabric label before buying anything.

If a panel is wetting out rather than beading, that is the water-repellent finish on the outer face rather than the coating that provides the hydrostatic head figure. The two are separate treatments with separate products, and both makers publish instructions that govern how they are applied.