Vapor Barrier Clothes and Bag Liner

3:35 p.m. on October 17, 2008 (EDT)
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Bill, and anyone else who knows about this stuff, we are having a discussion on TLB about vbl clothes. I have read about vbl for years, but never tried it since I really haven't been out in ultra cold weather which is what it seems to be made for.

Jack Stephenson was a big proponent of vbl and his company sells vbl clothes that basically look like people shaped industrial strength plastic bags. I'm sure other companies make similar stuff.

I read Stephenson's explanation of how it works on their website, but it seems to me that if you are skiing or snowshoeing and generating a lot of heat, then you would want to be wearing something breatheable so the heat and sweat could escape.

Once you stop moving, then the heat production slows down after a few minutes and therefore, you put on a jacket of some sort and maybe a hat to insulate you and retain the lower level of heat you are generating.

But, if you are wearing a vbl shirt or pants, for example, while skiing, doesn't all of the heat and sweat you generate stay inside the jacket or pants and you get hot and wet? Isn't the point of breatheable fabrics like eVent or Gore-tex to prevent that from happening?

I can see the vbl theory working at night, because you don't want your body moisture you are "outgassing" for lack of a better term to wet your bag from the inside,but it just doesn't make sense to me if you are moving and generating heat and sweat.

I have spent a lot of time underwater in a wetsuit, so I know how that works. Stand around in one in the hot sun for a few minutes and your temperature climbs quickly. To me, a vbl works about the same way, except in a wesuit, you are actually heating up a thin layer of water that keep you warm because it is insulated from the water surrounding you.

The eVent/Gore-tex theory vs. vbl theory can't both be right, can they?

Bill, were you using vbl stuff in Antarctica or on any of your other trips, like Denali?

What am I missing here?

7:25 p.m. on October 17, 2008 (EDT)
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Whether VBL works depends on the person and the circumstances. It's one of those things that may work well, sort of, or not at all, depending on you and the situation.

For me, the VBL socks work when skiing or climbing in very cold weather, but not in temperatures above about 0F [this is for inner wicking, VBL, outer heavy insulating (wool) socks].

VBL clothes do not work well for me when moving or other vigorous activity at any temperature - better in cold weather to have the standard inner wicking underwear, middle insulating layers, outer wp/b, although in some circumstances, like Antarctica, the outer layer works best if it is just a windbreaker during the hard climbing (even eVent doesn't breathe well enough for me if I am pushing hard up the hill, and Goretex or anything less breathable is hopeless).

VBL for the sleeping bag works quite well for me, providing I am in my wicking long johns and the temperature is below about 10-15F. Above that, I tend to feel somewhat clammy.

I know people who find VBL clothing works well for a ski tour colder than about 10F, and others for whom it doesn't work standing still, and still others (like me) for whom it works under certain conditions and not others. The theory is that your body will sense when to cut the sweating by the humidity next to your skin (Stephenson wrote words to that effect). But for me, it seems to be not the humidity, but the rate of heat loss - if that's just right, I barely sweat. Maybe it's because I grew up in hot climates (the Sonora Desert, Central America, inland Southern California), plus the time I spent in hot humid climates with 90/90 weather (Deep South, DC area in summers, Boston in summers). My body seems to say - it's hot, so sweat more to cool off. In Mississippi, it was like I had faucets all over, turned on full blast (in Arizona, the evaporation rate was fast enough to stay dry, not dripping like Mississippi).

So yes, eVent/Gtx and VBL are both right. You just have to take all parameters into account.

8:43 p.m. on October 17, 2008 (EDT)
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Thanks Bill. A Canadian guy on TLB was asking about it and he goes out in dead of winter in -30C weather regularly. I've tracked down some more info since I posted and what I've read pretty much agrees with your assessment.

I might try a vbl sock in a ski boot this winter, although my feet didn't get all that cold in the plastic boots I was wearing-Garmont Excursions, but worth a test.

A vbl in the sleeping bag might be an idea too, but my bag didn't seem to soak up that much moisture.

Stephenson has something posted on their site about Will Steger getting 35 lbs of ice in his bag over a month, but he was out in super cold weather in the arctic and I'm not going to be doing that.

9:09 p.m. on October 19, 2008 (EDT)
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Steiger and crew had 75 pound sleeping bags (non-stuffable) on their expedition to the North Pole, according to Steiger's report. Supposedly they averaged 2 pounds a day condensation, which pretty much agrees with the canonical 1 liter per night perspiration rate (plus another liter breathed out, hopefully through the face hole in your sleeping bag). I have a copy of his writeup (buried somewhere in the storage locker, awaiting resurrection after we get the house built). I was a contributor to both his trans-Antarctic and North Pole expeditions many years ago (got a very nice Goretex parka from the Antarctic trek in return for that donation), so I was on his mailing list for a while. That was what convinced me to first try out vbl sleeping bag liners.

One thing that helps, too, is to squeeze all that moist air out of the bag first thing on getting out in the morning, before it can freeze. That has seemed to keep the rate of frost accumulation down when not using a vbl.

10:20 p.m. on October 19, 2008 (EDT)
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Just reading along here trying to learn, by "squeeze all that moist air out" do you mean to just flatten the bag, or is their more to it than that?

Thanks

10:37 a.m. on October 20, 2008 (EDT)
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The Steger scenario is an extreme situation both in the duration of the expedition and the temperatures encountered. For most people in non-extreme temperatures and shorter trips a bag won't accumulate nearly that much frost, if any.

I've not found gore tex/event to work at all in Minnesota winters. Last winter I tried vb socks and they were fine - certainly better than sweat soaked boots. I also tried a vb bag liner and did not find the liner to be a problem, other than one more thing to deal with in a sleeping system. I've yet to try a vb top or bottoms, but would like to try these next. A Brynje mesh top underneath vb clothing may work well with warmer layers over the top if needed.

I find it much harder to stay cool when active in the winter than I do staying warm when sitting around.

4:14 p.m. on October 20, 2008 (EDT)
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"Squeeze the air out" means to roll the bag up tightl, starting at the foot and rolling toward the head. Most good sleeping bags have a very wind-proof outer shell and fairly breathable inner shell. If you try rolling the other way, you will find that the foot inflates and it is hard to squeeze the air out (same thing with stuffing the bag for carrying - stuff foot end into the stuff sack first and head end last - it's MUCH easier).

I agree with alan that weekend trips it doesn't matter a lot. But I have found that even on short trips, I stay a lot warmer on the 2nd and successive nights if I go through the effort to squeeze the moist air out on first getting out of the bag. And in warmer (15-40 F) temperatures, I find that the bag starts feeling damp in just a few nights, especially when it is humid, if I don't squeeze the moisture out.

Steiger's trip isn't really that extreme, especially if you are camping out in Minnesota winters.

July 30, 2014
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