RE: [Paddlewise] Down VS Synthetic

Quoting James <jimtibensky_at_fastmail.fm>:

> I use a vapor barrier on really cold nights, well below freezing, all the
> time.  I am a very cold sleeper who will sweat a lot when too warm.  The
> vapor barrier, strangely, does not get wet inside when I sleep.  I have
> never tried getting into it with wet clothes to dry them, as I do with
> other sleeping systems.
> 
> I know nothing about physics or anything else that might explain how this
> works, but it does.  I prefer to use a heavy fleece liner, but sometimes
> weight and space require the minimalist vapor barrier.  It is a
> convenient backup to have along.
> 

It's not a matter of physics as much as it is physiology. The body strives to 
maintain a constant level of humidity around it, so when you use a vapor 
barrier liner (VBL), your body reduces its production of insensible 
perspiration (water vapor) to maintain that humidity. Since water vapor 
contains heat (otherwise, it would appear as frost!), using a VBL prevents the 
loss of that heat while at the same time it keeps your body moisture out of the 
sleeping bag insulation.

For me the level of humidity in a VBL feels like that in a bathroom after a hot 
shower. I never feel wet inside (unless I get too warm), and my skin feels dry 
as soon as I slip out of the bag in the morning. The only thing I wear inside 
the VBL is polypro underwear, since I don't want moisture to accumulate in my 
clothing. Wet clothing inside a VBL would not dry out.

Once, on a beginner's winter camping trip, I used my VBL while sleeping next to 
a woman who was using two sleeping bags and no VBL. When I woke in the morning, 
my bag was wet with her perspiration where her outer bag touched mine, but 
otherwise mine was quite dry.

Chuck Holst

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