Bivi bag condensation

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Sub5mango

Tenderfoot
Oct 13, 2019
92
12
52
East Anglia
How much condensation should I expect on the inside of a bivi bag? Last night I slept my first night out in a bivi bag (in the garden!) I'm in the UK. There was a heavy dew and overnight lows were 7°c/ 45°f. My face was completely out of the bag. I was cosy warm but not hot. Inside of bivi was moist to touch, enough to make outside of sleeping bag damp, but no drips (Bivi is a macpac cocoon).
 

Nohoval_Turrets

Full Member
Sep 28, 2004
348
10
49
Ireland
Sounds about right. Still, dewy conditions make it difficult for the bag to breathe - the air is already overladen with moisture and isn't too inclined to take up more. A light breeze helps, which a sheltered garden often won't have. So yeah, your experience matches mine in similar conditions.

These are also the conditions where a tent is most likely to experience condensation issues.
 

Erbswurst

Native
Mar 5, 2018
1,455
527
Berlin
If you keep the face out of the bivvy bag you usually get no condensation problems, if the fabric of the bivvy bag is next to the sleeping bag. (Of course it has to be a breathable fabric.)

If there is to much space between them, you can get problems in colder conditions.

If you have a whet day you can get a bit moisture on the outer layer of the sleeping bag, but usually that doesn't become worse, you usually just heat it out.

If possible you should air the sleeping bag later and the bivvy bag " inside out" too.

But even if not, you shouldn't get a problem if you use the system every night. You just loose a bit body heat to dry the sleeping bag in the bivvy bag.

At home you should dry it all of course before you store it away.
 
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Sep 16, 2013
444
129
Rochester, Kent
How much condensation should I expect on the inside of a bivi bag? Last night I slept my first night out in a bivi bag (in the garden!) I'm in the UK. There was a heavy dew and overnight lows were 7°c/ 45°f. My face was completely out of the bag. I was cosy warm but not hot. Inside of bivi was moist to touch, enough to make outside of sleeping bag damp, but no drips (Bivi is a macpac cocoon).
Given the weather/atmospheric conditions that you've just described, I'd suggest that you'll get that issue with most bivvy bags. This particular time of year in the UK as well can be very damp indeed, which isn't going to help matters.
 
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