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#105021 - 10/21/08 06:03 PM Re: Vapour Barrier Clothing [Re: ringtail]
Earthling Offline

Registered: 02/22/03
Posts: 3228
Loc: USA
Also Dick, the venting on the neck and hem of a VB shirt is not like a regular crewneck. If it was then it would'nt allow the approairate moisture level to build and work with the VB shirt. Definitely tech clothing for the gear fiddler amongst us. I had a tone of it in the 70's, and then lost much of it while moving in the 80's <img src="/forums/images/graemlins/tongue.gif" alt="" /> along with some of my LP collection <img src="/forums/images/graemlins/crazy.gif" alt="" />

#105022 - 10/21/08 06:52 PM Re: Vapour Barrier Clothing [Re: Earthling]
Cesar Offline

Registered: 11/06/07
Posts: 217
Loc: El Paso, TX
quick question, how do you keep all your sweat from pouring out of your VBshirt onto the inside of your bag when you sit up. I guess the same goes for a VBLiner. You must need to get out carefully to keep from getting your bag wet. Also if its that cold that your body vapor can freeze in the down isn't it dangerous to unzip your bag and get out while wet at such low temps?
My gear is no where near lightweight

#105023 - 10/21/08 09:00 PM Re: Vapour Barrier Clothing [Re: TomD]
Paul Offline

Registered: 09/30/02
Posts: 778
Loc: California

Now back to our regularly scheduled program. From what I read, I though the idea was that once you reached essentially 100 per cent humidity in the vbl bag, you'd stop sweating because the evaporation would stop. Not so?

Tom, this is the basic theory ONLYas it applies to "insensible" perspiration, and ONLY if you are at an equilibrium temperature - not hot, not "sweating". If you are hot, and your body is producing sweat to cool itself off, you will continue to do so regardless of the humidity. Again, it's all about managing the insulation to acheive that teperature equilibrium. Not too hard to do for sleeping or sitting, VERY hard to do while active.

#105024 - 10/21/08 11:11 PM Re: Vapour Barrier Clothing [Re: Cesar]
phat Offline

Registered: 06/24/07
Posts: 4107
Loc: Alberta, Canada
quick question, how do you keep all your sweat from pouring out of your VBshirt onto the inside of your bag when you sit up. I guess the same goes for a VBLiner. You must need to get out carefully to keep from getting your bag wet.

The idea with a VBL liner is *not* to sweat a lot in it. As for a VBL shirt, rick's not talking about wearing this in the bag - he's talking abou wearing it while walking in subzero.
Of course you have to be careful.


Also if its that cold that your body vapor can freeze in the down isn't it dangerous to unzip your bag and get out while wet at such low temps?

If this were the case Canada would have never had human occupation because their bladders would have burst as we all steadfastly refused to leave our sleeping bags/buffalo robes. (then again I know I've had mornings that felt like that <img src="/forums/images/graemlins/smile.gif" alt="" />

it's not like you're sitting in the bag soaking - the problem is not that you are dripping - the thing you have to remember is this isn't that you're wet, it's just the natural water vapor that comes off your skin that freezes. Think about when you are in a single wall tent - you're not wet, but there's a bunch of moisture on the inside condensed in the tent. A lot came from your breathing, but some came from water coming right off your skin. In really nasty cold, that water doesn't go up and condense on your tent, it condenses, then freezes,
inside the sleeping bag. and if it's down that can really suck. The VBL doens't leave you sweaty (or it shouldn't in a bag) It should leave you comfortable, not dripping.

and as for getting out - you can always get out in such weather - you just can sit outside naked and wet with no chance of getting dry and warm.
Any fool can be uncomfortable...
My 3 season gear list
Winter list.
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#105025 - 10/22/08 08:43 AM Re: Vapour Barrier Clothing [Re: phat]
alanwenker Offline

Registered: 02/04/03
Posts: 812
It's worth keeping in mind there is a large difference between getting out of one's bag and vbl with one's long underwear slightly damp (but warm) versus being totally sweat soaked with perspiration running down one's body and a pool of sweat inside the vbl. Frequently in vbl discussions I think the later image is what is conveyed, but in my case the former image is what I've experienced. I'm not referring to vb clothing worn when active, but mainly just in a sleeping mode where one is not moving around. I'm 75% certain I like the vbl for sleeping, but have to make time to experiment with vb shirts.

#105026 - 10/23/08 02:03 PM Re: Vapour Barrier Clothing [Re: Rick]
whcobbs Offline

Registered: 10/14/02
Posts: 227
For several years I have used a hooded silnylon rainsuit as a vb suit for sleeping in subfreezing temps. Lightwt polypro longjohns go next to skin, then the rainsuit, then a stretch layer (pp/Lycra balaclava, power stretch ski suit or alternately polypro stretch bike jersey and winter polypro biker tights, then the insulated clothing ( Parka, insulated pants, finally a 2lb synthetic overbag. This scheme will dry out the damp clothing from the day's hike with body heat and dissipate the moisture through the bag. Do not try it with a down bag or with temps above freezing! Lightweight.

#105027 - 10/23/08 03:14 PM Re: Vapour Barrier Clothing [Re: whcobbs]
OregonMouse Offline

Registered: 02/03/06
Posts: 6430
Loc: Gateway to Columbia Gorge
My experience with using a vapor barrier in a sleeping bag is limited to six below-freezing nights in the Rockies last summer. After the first frosty morning, when my down bag was distinctly damp, I remembered what I'd read about vapor barriers and tried wearing my non-breathable (silnylon) rain jacket and pants to bed over my base layer. It worked just fine. I avoided getting sweaty in the early evening by leaving my sleeping bag open (please remember that this was a Rocky Mountain summer, not a Canadian winter!). Usually after the second time I woke up (one of the problems of aging is that I have to get up several times during the night), I'd zip the bag up. By about 2-3 am, I'd have to snug up the draft collar in my sleeping bag. A couple of nights I was borderline cold about 5-6 am. Those were the nights my dog's water dish froze solid, leaving one puzzled dog in the morning! I didn't sweat and didn't even feel damp. My sleeping bag stayed dry, too. I normally do a lot of sweating, so this was a big surprise to me!

Edited by OregonMouse (10/23/08 03:15 PM)
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey

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