Thread: Condensation on Sleeping Bag

Interesting thread. Hunted with 2 different people over the years who had fairydown 20 below sleeping bags. They would wake up most mornings without fail with the outside of their bags wet, more so in colder weather.
Ive used several different makes of bags over the years and have only encountered this problem with a marmot lithium sleeping bag, heavy bag for winter use only... Although this bag has hardly been used, I dont use it anymore.
Currently using a mamot phase 20 plus macpac bags without any issues..

Have you contacted macpac to see if they can shed any information on what maybe the cause of it????

Originally Posted by gonetropo

stop watching porn before bed time

There’s always one

Sometimes suffer the same thing, fucking frustrating when moving camps each day

A thought that just popped into my head - is your sleeping bag being stored in a dry environment? Could it be taking on some moisture at home and then it’s coming out when you heat it up?


Sent from my iPhone using Tapatalk

best guess is poor airflow in tent with condensation latching on to everything that's cold, tent walls and bag exterior. The problem is the bag is too good and none of your body heat is getting through. One of the reasons I moved on to hammocks and tarps.

It’s just simple condensation. Obviously your bag is warming right through to outer shell and cool moist air, in the tent is condensing on outer shell. Slap a lightweight waterproof tarp on top of bag or start using a bivvy bag.

Originally Posted by Smiddy

A thought that just popped into my head - is your sleeping bag being stored in a dry environment? Could it be taking on some moisture at home and then it’s coming out when you heat it up?

I was just wondering about that too.

As far as I can remember I've only had wet top of sleeping bag in the morning is when I've been in a bivy bag or under open skies and got dew on it.

With a good bag in cold conditions I've had frost/ice on top but the bag insulated well enough that it didn't melt.

Originally Posted by gonetropo

stop watching porn before bed time

I like to leave it playing at night too it helps me sleep.

Are you fully closing up the tent at night? I have found that built in vents are almost never sufficient on their own. I tend to leave the insect mesh exposed and air gaps between fly and inner.




Sent from my iPhone using Tapatalk

Originally Posted by Cliff

It’s just simple condensation. Obviously your bag is warming right through to outer shell and cool moist air, in the tent is condensing on outer shell. Slap a lightweight waterproof tarp on top of bag or start using a bivvy bag.

Expensive exercise to go buy a bivvy bag just to test the theory. I will try a top sheet maybe.

Originally Posted by YosemiteSam

best guess is poor airflow in tent with condensation latching on to everything that's cold, tent walls and bag exterior. The problem is the bag is too good and none of your body heat is getting through. One of the reasons I moved on to hammocks and tarps.

I dont think its this as it happens with my tarp. I dont think you will find a more freeflowing tent than a tarp set up as an A frame.

Originally Posted by Smiddy

Sometimes suffer the same thing, fucking frustrating when moving camps each day

A thought that just popped into my head - is your sleeping bag being stored in a dry environment? Could it be taking on some moisture at home and then it’s coming out when you heat it up?


Sent from my iPhone using Tapatalk

I've hung the bag up in the wardrobe now to see if that helps.

Originally Posted by kiwioutdoors

Are you fully closing up the tent at night? I have found that built in vents are almost never sufficient on their own. I tend to leave the insect mesh exposed and air gaps between fly and inner.

Sent from my iPhone using Tapatalk

I usually leave the vestibule open partially if possible and have tried with a tarp that has great ventilation.

Originally Posted by Cliff

It’s just simple condensation. Obviously your bag is warming right through to outer shell and cool moist air, in the tent is condensing on outer shell. Slap a lightweight waterproof tarp on top of bag or start using a bivvy bag.

Just to clarify, I don’t think it will be moisture from the outside air, as this would only condense on cooler surfaces (think beer cans). What’s happening is interstitial condensation, similar to what happens in the walls of a house.

Air heated by your body gets drawn to the outside, taking vapour with it. As it contacts the outside it cools and can’t hold as much water, so it dumps it. Look up ‘relative humidity’.

If you’ve got condensation on the outside then the bag is doing it’s job, and not allowing it to wick back into the absorbent filling. More of a worry if the condensation occurs on the inside of the outer shell.

You should dry it as early as possible though, DWR coatings can only do so much. If you must pack it up damp, then take it out as soon as you set up your next camp.

Originally Posted by mopheadrob

Just to clarify, I don’t think it will be moisture from the outside air, as this would only condense on cooler surfaces (think beer cans). What’s happening is interstitial condensation, similar to what happens in the walls of a house.

Air heated by your body gets drawn to the outside, taking vapour with it. As it contacts the outside it cools and can’t hold as much water, so it dumps it. Look up ‘relative humidity’.

If you’ve got condensation on the outside then the bag is doing it’s job, and not allowing it to wick back into the absorbent filling. More of a worry if the condensation occurs on the inside of the outer shell.

You should dry it as early as possible though, DWR coatings can only do so much. If you must pack it up damp, then take it out as soon as you set up your next camp.

Agree in part, there'll be a heap of different forces at work, in short the bags wetting out (from a form/s of condensation) and as Stocky mentions that moisture is wetting through the down as well.

Other things to consider, are you sleeping in dry clothes (?) damp clothes will produce more vapor. Are you going to bed hot and filling bag with vapor quickly? Sometimes sticking an arm or leg out to cool down, results in your body feeling the limb cooling down, fires up the furnace to protect the core and voila, you're producing more vapor.

As some others have said it’s warm moist air condensing on a cooler surface. The physics of sleeping in a tent!

Try to reduce the moisture you take inside inside the tent eg wet boots, pack, clothing, cooking etc and try maximise ventilation to remove the moist air (you breathe out a heap of it overnight) by opening all vents, raising the fly if poss and leaving doors open to increase air flow
Where you pitch can also cause issues eg next to streams, on wet ground for example.

A trick you can do if it’s mainly wetted down at your feet (from brushing up against the inner fly) is to zip up your waterproof jacket and slide your bagged feet into the bottom of the jacket. Keeps the outer bag dry. Hope this helps...

Originally Posted by mopheadrob

Just to clarify, I don’t think it will be moisture from the outside air, as this would only condense on cooler surfaces (think beer cans). What’s happening is interstitial condensation, similar to what happens in the walls of a house.

Air heated by your body gets drawn to the outside, taking vapour with it. As it contacts the outside it cools and can’t hold as much water, so it dumps it. Look up ‘relative humidity’.

If you’ve got condensation on the outside then the bag is doing it’s job, and not allowing it to wick back into the absorbent filling. More of a worry if the condensation occurs on the inside of the outer shell.

You should dry it as early as possible though, DWR coatings can only do so much. If you must pack it up damp, then take it out as soon as you set up your next camp.

I agree with @mopheadrob. If the 'moisture' is not the result of masturbation and flatulence then it must be condensation, formed when the warm moist air hits the 'dew point' on the cold outside of the bag. A solution would be to lay a brush cotton sheet over the bag while sleeping which will slightly insulate the outside of the bag thus moving the 'dew point' to the top surface of the sheet instead of the bag. You will have a wet sheet in the morning but a dry bag, you dirty depraved deer shagger.

Originally Posted by gonetropo

stop watching porn before bed time

Interestingly, Heath Ledger complained of sleeping bag condensation whilst making a certain movie