Wednesday, Jun 29, 2011 at 10:22
Keep your head outside the tent.
To understand why it happens you must understand why we get rain and storms.
Air can only hold so much moisture. Warm air hold more moisture than cold air. Say for example Air @30 deg C can hold hold max 10ml of water per cubic metre, while air @10 deg C can hold only 5ml of water.
So, if your air @ 30degC holds 5ml of water it is said to have 50% "relative humidity." If that air is cooled to 10degC it still has the 5ml of water in it but the relative humidity is now 100%. If the air temperature drops below this temperature, the air will need to release some of the water vapour and form water droplets. So if the air is cooled to say 2degC it may only hold 2ml of water and the remaining 3ml will be in the liquid form and will fall (out of the sky.)
When you are in your tent sleeping, the air you breath out is warm and full of moisture. When this warm air passes by something that is cold, like tent poles, tent lining etc, its temparature drops and water droplets are released.
What could possibly be happening in your case is condensation is occuring on the inside of your tent ceiling and dropping on you. I think it is unlikely that condensation would occur on the sleeping bag itself.
I heven't heard of any great ways to prevent this other than raising the temperature of the air in the tent and therefore the tent itself. Try putting a blanket over your tent above the area where you are sleeping to increase the temparature of it in that spot
. Else, stop putting warm, moist air into it.
Hope that's clear enough.