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vapor barrier liners for cold temperatures

Posted: Wed Jan 12, 2011 4:14 pm
by zelph
I found this article very informative by Andrew Skurka.

http://www.andrewskurka.com/advice/tech ... php#images

Re: vapor barrier liners for cold temperatures

Posted: Wed Jan 12, 2011 6:11 pm
by Ridgerunner
Good information! Sounds like there is a lot of regulating your clothing to keep yourself dry but being able to keep your layers dry is a nice benefit. ;)

Re: vapor barrier liners for cold temperatures

Posted: Wed Jan 12, 2011 6:13 pm
by sudden
Very informative.

thx for the link

Re: vapor barrier liners for cold temperatures

Posted: Thu Jan 13, 2011 1:34 pm
by zelph
It's a good article to read to read several time.

(quote)

Effects and Benefits

The principal effect of a VBL is stopping the transmission of insensible and sensible perspiration, i.e. sweat, away from your body, effectively creating a microclimate between the VBL and your body. (Without a VBL, perspiration would move away from your body and through outer layers (if applicable), and then hopefully evaporate into the atmosphere.) This entrapment of moisture has three benefits:

First, perspiration will not reach outer layers like a windshirt, insulated parka, or sleeping bag. This is hugely important because in cold conditions your perspiration will often stay in these layers: the dew point is somewhere between your body and the outside atmosphere, and your perspiration will condense from water vapor into actual water, thus wetting the layers. This will cause down and synthetic insulations to ultimately collapse. And it will cause unwanted evaporative heat loss with other fibers like polyester, nylon, and wool.

Second, the wearer is always keenly aware of their rate of perspiration, and they are better able to thermoregulate properly as a result. Without a VBL, you might begin to overheat and sweat profusely without fully realizing it. This will soak layers and cause dehydration, which will lead to poorer circulation and lower respiratory efficiency; you may also waste more time and fuel melting snow to get water. With a VBL, however, this scenario is far less likely to happen: you will notice the rainforest-like humidity level in the microclimate -- or, if you really overdo it, the sweat dripping down your back -- and you will react by removing layers or increasing ventilation.

Finally, evaporative heat loss is minimized. All forms of heat loss should be carefully managed in cold conditions, and a VBL is an effective way in which to manage evaporative heat loss. (The other types of heat loss are conduction, convective, and radiation.) To illustrate this point, imagine how it feels to work up a sweat while snowshoeing up a mountain and then resting for a few minutes at the cold, windswept summit. Brr...

Re: vapor barrier liners for cold temperatures

Posted: Thu Jan 13, 2011 2:10 pm
by ConnieD
Skurka, ...the wearer is always keenly aware of their rate of perspiration, and they are better able to thermoregulate properly as a result. Without a VBL, you might begin to overheat and sweat profusely without fully realizing it.
This is why my first layer is silk, or, silk-wool blend or a soft "smartwool".

I feel the dampness of perspiration more quickly, and, I have the added benefit I maintain that layer of "insensible moisture" so essential to skin for proper body thermo-regulation.

I do not use any "dry" or "drying" fabric first layer, not even in the high mountain desert.

The only time I have successfully used a VBL is inside a sleeping bag in winter.

I am of the opinion, a VBL only works properly in winter cold weather conditions, resting inside my sleeping bag.

There is one other circumstance, stream crossing. The VBL over-booties sold are great for stream crossing, if not especially durable, they are very lightweight. I make my own.

Re: vapor barrier liners for cold temperatures

Posted: Thu Jan 13, 2011 2:17 pm
by ConnieD
Skurka, To illustrate this point, imagine how it feels to work up a sweat while snowshoeing up a mountain and then resting for a few minutes at the cold, windswept summit.
Never! Do not sweat!

Strip to your longjohns and a windshirt, if necessary. Wear suspenders, open up your pants for ventilation.

When you stop, button-up again, add all those extra clothing layers from your pack.

Do put on your premium down "belay parka".

Re: vapor barrier liners for cold temperatures

Posted: Thu Jan 13, 2011 2:32 pm
by ConnieD
Skurka, Winter Sleep & Clothing Systems

During the deep winter I use vapor barrier liners (VBL's) in order to reduce evaporative heat loss and prevent my insulation from "collapsing." VBL's contradict modern emphasis on breathability -- they are made of non-breathable fabrics that do not permit the transfer or moisture.

To understand how VBL's prevent insulation collapse, let me explain two scenarios rating to sleeping bags assuming you were not using VBL's. In warm conditions your perspiration moves to the outside of the bag and evaporates, keeping the insulation mostly dry. But in cold conditions (starting at around 15-20 degrees) your perspiration moves towards the outside of the bag but hits the dew point before getting there (it's so cold that the dew point is actually inside your insulation). The perspiration turns into moisture and soaks the insulation; with every passing night your sleeping bag becomes wetter, heavier, and less able to insulate.

If you wear a VBL, you can prevent your perspiration from entering your sleeping bag insulation at all. And the perspiration does not just build up inside the VBL -- your skin senses that the "micro climate" between it and the VBL is fully saturated with moisture, and so it stops perspiring in that area.
http://www.andrewskurka.com/advice/reco ... winter.php

This is his website page.

Re: vapor barrier liners for cold temperatures

Posted: Thu Jan 13, 2011 2:43 pm
by ConnieD
I am very passionate about this issue: sweating and getting chilled, because hypothermia is much more dangerous than most of the other risks in backpacking.

Skurka is correct about the moisture build-up in a sleeping bag in "shoulder season" or in winter cold conditions.

It is possible to wear a VBL shirt, and "sweat" but it is, in my opinion, a bad idea unless you "towel off" inside the VBL. Proper full body thermo-regulation is vital.

I would rather know what the best Iditerod folks wear, from the inside out.

Here are Andrew Skurka's guidelines:
RealFeel Temperature. I do not necessarily use AccuWeather's patented index, but I think the idea is useful -- it is a measure of all of the environmental factors that affect how warm or cold I am. This would include ambient air temperature, wind, sun exposure, precipitation, humidity, and ground cover. I find that I can begin to wear VBL gloves in temperatures below 40 degrees F, a jacket and socks below 20, and pants below 10. If it is windy and/or cloudy, if precipitation is falling (particularly cold rain, sleet, or wet snow), and/or if I am walking on or through snow or ice, then I may be comfortable wearing VBL's in warmer temperatures. If the conditions are opposite (no wind, lots of sunshine, no precip, and dirt or grass ground-cover), then it may have to be colder before VBL's can be worn comfortably.
My "VBL pants" are rain chaps, loosely worn. ;)

All that said, I have the PSolar mask because it takes up little space in my pack. It does not restrict my breathing, even with exertion. If you like, choose the PolarWrap Warm Air Mask or Full Head Cover or Exchanger II.

If I feel really cold, I will use any one of these specialized masks so my warmth does not escape with each breath, add condensation moisture inside the bivvy, tent, or tarp shelter, or get any part of my sleep system wet.

This is an effective method to avoid evaporative heat loss.

Re: vapor barrier liners for cold temperatures

Posted: Thu Jan 13, 2011 5:35 pm
by sudden
I'm gonna need a sham-wow suit when I finally get back on the trail. Going through physical therapy now and can't believe how quickly I overheat. :oops:

Re: vapor barrier liners for cold temperatures

Posted: Thu Jan 13, 2011 6:44 pm
by zelph
Here is what he says about "when not to wear the barrier"


4. Effort intensity. In order to avoid over-sweating while using VBL's, I must be attentive to body heat generation and be willing to regulate it.

This is fairly easy during steady, low aerobic activities like hiking, snowshoeing, mountaineering, ski touring, snowmobiling, ice fishing, etc. The task becomes more difficult for activities like alpine skiing and climbing, when periods of intense exercise are followed by periods of sedation, e.g. leading a pitch and then belaying a climbing partner up to the anchor.

For high aerobic activities like running, skate skiing, or alpine touring (AT) racing, I find it almost
impossible to avoid sweating and therefore VBL's are probably inappropriate in this context.

by sudden ยป Thu Jan 13, 2011 5:35 pm
I'm gonna need a sham-wow suit when I finally get back on the trail. Going through physical therapy now and can't believe how quickly I overheat. :oops:
I can just picture you wearing that suit :lol: