Sleeping Bag wet from condensation.

Submitted: Tuesday, Jun 28, 2011 at 16:19

Humphrey57

Hi folks. I am new to this forum so forgive me if this has been covered. I searched and found nothing relevant.

I have a Roman brand king size bag with a nylon cover..

It is ok when used inside but under canvas develops copious amounts of condensation on the outside of the bag. With more ventilation it is worse.

The bag gets wet through and I threw it off and grabbed a blanket last weekend at Sawtell.

I nearly need a tarp over it to stop the water saturating it.
I may as well slept in the rain.

Cheers Phil


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AnswerID: 458712   Submitted: Tuesday, Jun 28, 2011 at 21:33

willawa replied:

may be you should buy a "swag" you'll find it much better.

Cheers

Harold J
willawa (NSW)
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AnswerID: 458723   Submitted: Tuesday, Jun 28, 2011 at 23:23

Member - Chris and Lindsay (VI replied:

Hey Phil, I would take it back for a refund if you can. Chris.
I took the road less travelled, and that made all the difference.
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FollowupID: 732250   Submitted: Wednesday, Jun 29, 2011 at 07:27

Humphrey57 posted:

All I want to know is why it happens.
I am sure others are in the same situation.

I am inside a canvas tent.
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FollowupID: 732254   Submitted: Wednesday, Jun 29, 2011 at 08:07

Humphrey57 posted:

What is the road less travelled?
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FollowupID: 732258   Submitted: Wednesday, Jun 29, 2011 at 08:17

Polaris posted:

Hi Humphrey57 ....

"All I want to know is why it happens."

Simple thermal physics. Your body warms the inside - so the cold air forms condensation on the outside.

SB's with better external waterproofing will form more condensate than those that are less efficient. The less efficient ones will absorb the condensate and you may not notice it.

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FollowupID: 732261   Submitted: Wednesday, Jun 29, 2011 at 09:23

Humphrey57 posted:

Ok. At first my bag feels wet on the outside.
Then progressivlly gets wetter until it is wet right through.

The outside is not waterproof. Am I correct?
So sleeping under a tarp is a good idea?

.
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FollowupID: 732404   Submitted: Thursday, Jun 30, 2011 at 10:32

Rob! posted:

Yes and No.

Contrary to my previous reply, the condensation that may be occuring on your sleeping bag is likely to be from the moisture in the night air because, as you said, the more it is ventilated the worse it gets. Putting a tarp over yourself will help, but if your head is under the tarp you will get condensation on the inside of the tarp for the reason I described above.

R.
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AnswerID: 458735   Submitted: Wednesday, Jun 29, 2011 at 08:10

Humphrey57 replied:

All I want to know is why it happens.
I am sure others are in the same situation.

It only seems to do it in winter when the stupid bag is really needed.
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FollowupID: 732262   Submitted: Wednesday, Jun 29, 2011 at 10:22

Rob! posted:

Short answer:
Keep your head outside the tent.

Long answer:
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.

R.
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FollowupID: 732275   Submitted: Wednesday, Jun 29, 2011 at 12:42

Humphrey57 posted:

Thank Rob. Now I know why I can try a few different things.

It seems to be worse in bigger tents with more ventilation.

I was in a 3x3 mtr Serengheti on the week end and in the past a 14x14 marquee.

When in my caravan I just have sheets and a blanket.

Cheers Phil
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FollowupID: 732390   Submitted: Thursday, Jun 30, 2011 at 08:58

Sigmund posted:

There are now water-resistant breathable bags you can slip your sleeping bag into to increase warmth and reduce water absorption.

If you want to spend up big, there are also sleeping bags with shells of this material that does the same job.
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FollowupID: 732395   Submitted: Thursday, Jun 30, 2011 at 09:27

Humphrey57 posted:

Maybe there is a market for a goretex blanket.
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FollowupID: 732398   Submitted: Thursday, Jun 30, 2011 at 09:50

Sigmund posted:

Vapour transmission with Goretex and the like depends on the pressure difference - warm humid inside, colder and dryer outside.

What's happening here as posted is condensation on the bag from moist cool air.

Another option would be to spray some waterproofing stuff on the bag shell; that'll reduce moisture absorption.
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FollowupID: 732401   Submitted: Thursday, Jun 30, 2011 at 10:24

Humphrey57 posted:

That's a great idea Sigmund. I will track some down'

I hope this has helped some others
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FollowupID: 732409   Submitted: Thursday, Jun 30, 2011 at 12:26

Sigmund posted:

Happy to help.

I've got 4 down and 1 synth bags, for sub-zero to mild nights.

Some condensation is inevitable. My old Paddy Pallin bag, japara covered, looks like I've been incontinent :-{

I've always been in small hike tents. My take is that it's water vapour off the body that condenses when it breathes through to the shell; but many mornings the foot of the bag is against the tent when I wake up, and is pretty damp, so there are other things going on as well.

Anway, re a proofing treatment, speak to Roman or a decent bushwalking shop since there are options. Even one where you wash the whole bag in it.

Good luck.
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