The Vapour Barrier Liner (VBL) thread.

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Imagedude

Full Member
Feb 24, 2011
1,973
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Gwynedd
This thread is for people to share their experiences of using vapour barrier liners. The thread may also be used to ask questions about VBL.

My only experience of VBL was the nose hair searing smell that came from Teepee's VBL socks in Norway.:yuck::stretcher:

Could a bivi bag be used inside a sleeping bag as a VBL?
 

Teepee

Bushcrafter (boy, I've got a lot to say!)
Jan 15, 2010
4,116
4
Northamptonshire
Yes, VBL liners are sold for sleeping bags. I have the Blizzard bag and a thinner reflective emergency liner which would work.

My thoughts are that getting out of the VBL liner will be quite a shock in the morning in slightly damp thermals, so I opted for VBL clothing.

For this winter in Sweden, I have 2 pairs of RBH custom VB socks and an aluminium coated polyester sauna suit. I can get out in the morning without being subjected to the cold in slightly damp clothes.


IME, there are 4 rules for using VBL clothes;
1. Dont sweat in them
2. Dont sweat in them
3. Avoid sweating in them at all costs
4. Don't pick up my worn socks without pliers or a stick.
 

Shewie

Mod
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Dec 15, 2005
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My only experience of VBL was the nose hair searing smell that came from Teepee's VBL socks in Norway.:yuck::stretcher:
I've suffered the same once or twice, it kind of put me off the whole idea :)

I get the theory of preventing moisture getting into the important stuff, but surely it can't be good to be stewing in your own sweat the whole time? The idea of a clamming plasticky layer next to the skin doesn't really do it for me. The bag liner is a possible interest, but you sleep in the buff I guess to prevent getting soggy base layers? I've looked at the Blizzard bags a few times, and those Reactor bags but never pulled the trigger on one.

Back on the clothing again, would you wear the socks, top and leggings for an active day or is it for when you stop at camp? I'm guessing even down as low as it gets over here, there's still going to be perspiration. AS talks about using them for walking in temps around -6 to -12*c, I'd still be sweating at those temps if I hillwalking.

EDIT:
Just re-read that article and he's answered a few of my questions, still not sure it's for me but I wouldn't mind trying it one trip. I'll maybe pick up one of those plastic chemical overalls :)
 
Last edited:

maddave

Full Member
Jan 2, 2004
4,177
35
Manchester UK
For this winter in Sweden, I have 2 pairs of RBH custom VB socks and an aluminium coated polyester sauna suit.
Why have I got an image of Scousers in my head?? :lmao:

I'm out on VB though... I've never bothered in the past and I think skin being moist in sub zero temps won't be pleasant. I'll bring some polythene bags and have a go, but it just seems unnatural not to let your feet breathe
 

Imagedude

Full Member
Feb 24, 2011
1,973
10
Gwynedd
I'm told that I breath out through my **** quite a lot at night. I'd need my VBL gimp suit to be fitted with a 1 way valve and a length of hose!
 
I have had such great enjoyment in using traditional, vapor permeable, natural fibers that I just can't bring myself to try VBL clothing. Next month I will have a chance to listen to an expert while we all try to keep from freezing in northern Minnesota. Maybe I will learn something...

- MacEntyre
 

John Fenna

Lifetime Member & Maker
Oct 7, 2006
21,884
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Pembrokeshire
Many many years ago I tried a cheap VBL suit (actually a super cheap set of light weight waterproofs) in my sleeping bag in very frosty conditions.
I do not recall being any warmer than I would have been without it ... what I do remember is being VERY uncomfortable!
I do not even like wearing classic PJs as I find they bind on every joint in the body and cut off circulation - the same was true with the cheapo VBL plus the "feel" of the fabric was most unpleasant and the "perfume" the VBL gained was an aquired taste.
For me the discomfort of the VBL outweighed and warmth gain and pack weight reduction and I went back to wearing nowt in my bag most of the year and nice comfy, stretchy, breathable thermals (preferably wool) in bitter conditions.
A VBL bag liner as oposed to a suit may be a better option but my experience of VBL has put me off the idea....
 

rg598

Native
VBL are essential in cold weather extended trips. The reason is that the breathability of materials becomes somewhat irrelevant at low temperatures (anything below 20F/-7C). As the warm water vapor and sweat move away from your body, they encounter the cold temperature from the outside. In low temperatures, that cold area ends up being somewhere inside the insulation layer. The result is that the valor condenses and then freezes inside the insulation before it gets a chance to exit the clothing, no matter how breathable it is.

A VBL stops the moisture from moving away from your body, keeping the insulation dry. This is not a big deal for a trip that will last a day or two, but for longer outings, if you are not using a VBL, or manage to dry out the insulation each day, that insulation will become useless.

Usually you don't wear VBL directly on your skin. You typically have it over a base layer. You get used to it very fast. It's no different than being wet from sweat. The same principle is used for example in the US military snow boots (bunny boots). They have a built in VBL in that the insulation is fully enclosed in rubber. They are intentionally not breathable.

I use a VBL in my sleeping bag (in cold weather extended trips), and in my boots. Boots are very hard to dry, and without VBL in is impossible to keep them from getting wet. There is nothing like waking up to see the ice that has formed on your sleeping bag to motivate you to use a VBL.
 

mrcharly

Bushcrafter (boy, I've got a lot to say!)
Jan 25, 2011
3,246
33
North Yorkshire, UK
rg598's description makes sense.

I've read a description of using Buffalo system that offers an alternative approach to the problem.

A lighter buffalo bag with pertex cover is used inside a thicker bag. The idea is that you ensure the condensation line/layer is outside the pertex of the inner bag, hence keeping ice and dampness away from you.

Sleeping in a goretex or similar bivvi bag inside a synthetic sleeping bag would have a similar effect.
 

Keith_Beef

Native
Sep 9, 2003
1,331
237
51
Yvelines, north-west of Paris, France.
VBL are essential in cold weather extended trips. The reason is that the breathability of materials becomes somewhat irrelevant at low temperatures (anything below 20F/-7C). As the warm water vapor and sweat move away from your body, they encounter the cold temperature from the outside. In low temperatures, that cold area ends up being somewhere inside the insulation layer. The result is that the valor condenses and then freezes inside the insulation before it gets a chance to exit the clothing, no matter how breathable it is.

A VBL stops the moisture from moving away from your body, keeping the insulation dry. This is not a big deal for a trip that will last a day or two, but for longer outings, if you are not using a VBL, or manage to dry out the insulation each day, that insulation will become useless.

Usually you don't wear VBL directly on your skin. You typically have it over a base layer. You get used to it very fast. It's no different than being wet from sweat. The same principle is used for example in the US military snow boots (bunny boots). They have a built in VBL in that the insulation is fully enclosed in rubber. They are intentionally not breathable.

I use a VBL in my sleeping bag (in cold weather extended trips), and in my boots. Boots are very hard to dry, and without VBL in is impossible to keep them from getting wet. There is nothing like waking up to see the ice that has formed on your sleeping bag to motivate you to use a VBL.
I've got a pair of those US arctic boots, but I really only wore them for short times when on sking trips in February in Vermont. They are big, bulky, not at all heavy compared to the leather boots of my childhood and teenage years, but very, very warm. absolutely not breathable, and if I was going to be camping out and hiking, I would definitely want to find a way of making sure that they dried out completely overnight. Maybe a cotton bag of rice or buckwheat grains that I could heat up and dessicate over the fire and then leave inside the boots to absorb all the moisture.

But then again, those boots have practically no textile lining inside, so almost all the moisture that could accumulate inside the boot would be on your sock, that you would dry overnight anyway.

I imagine VBL being somewhat like a wetsuit, in that it uses a layer of moisture trapped against the skin as part of an isulation layer.
 

Grey Owl

Tenderfoot
Nov 26, 2006
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voyagetothebay.cauc.ca
Vapour barriers are a contentious issue, some despise them, some admire them. Before I launch into my opinion on them, I'd like to thank rg458 for articulating a great response. Although I respect the opinion/experience of a couple other folks that have responded, my intention is to offer some personal insights, and perhaps a little science. We will start with recommendations, continue with some discussion and then reflect backwards on the initial recommendations.

Recommendations:
Vapour Barriers are most effective under the following conditions.
  • -20C or colder
  • When metabolic heat production is minimized
  • Used over a thin insulative layer
  • Avoid during vigorous movement

Some Science:

We humans have a challenge, we are primarily a tropical creature, that really only thrives when our bodies are subjected to tropical conditions. At the skin/atmosphere interface our body attempts to maintain a humidity of 70-80%. This is achieved through vaporisation of water, or what we typically call sweating. But in reality, what we think of as sweating, is really excessive vaporisation followed by condensation on the skins surface or in our clothing. While we are exercising during the day, we are typically producing large quantities of metabolic heat, in order to maintain an ideal temperature our body reacts by vaporizing additional moisture, and we behaviourally should remove layers to reduce insulation and allow the metabolic heat to dissipate as water vapor before it condenses.

In the winter or cool weather, most of us will wear a base layer, either synthetic or woolen. When functioning properly this layer is capable of 'wicking' the water vapor away from our skin before it has the opportunity to condense as liquid sweat, soak our clothing and possibly result in overcooling. However, once we are at rest our body is producing much less metabolic heat, yet it still needs to maintain the 70-80% humidity at the skin/atmosphere interface. In cold climates we now have some challenges. Now that we have all that information out on the table, let's put it together. Our base layer itself is working against our bodies innate tendency to maintain a high humidity at the skin surface. As we release needed water vapor, our clothing is busy attempting to move this required vapor away from the skin.

To create water vapor is an enormously energy intensive endeavour. To be precise 4.186J are required to raise 1g of water 1C. But to turn that same gram of water into vapor requires 2,257 j/g. The heat of vaporization is not being used to raise the temperature of water, but merely to break the intermolecular bonds between adjacent molecules and allow the to escape as water. What does this mean to us? The more you sweat, the more heat you lose, the more energy you lose. Or another way, the more energy utilized to create water vapor, the colder you will be. So to conserve heat, we need to reduce the quantity of water lost through vaporisation.

Vapor Barrier (VP) Function and Usage:
At the simplest level, a VP restricts the loss of water vapour, and by default creates a microclimate with 100% humidity. If we are encased in 100% humidity in our environment, then our body does not need to release additional moisture to achieve the desired tropical skin level condition.

If we are exercising and producing large quantities of metabolic heat, we are also likely to need to cool our bodies via sweating. Sweat is released as water vapor, the creation of water vapour results in heat loss (aka. as cooling), etc. If you are using a vapour barrier during intensive exercise, then you will be trapping large quantities of condensed vapor (sweat) in your clothing and against your skin, and will likely suffer from a few olfactory challenges (see posts by: Shewie and Imagedude) and potentially debilitating "pruning".

On the other hand, when we are sleeping in cold conditions the retention of heat energy is tremendously important and we are unlikely to be producing any excess metabolic heat. Our bodies will only be vaporizing adequate moisture to maintain the ideal skin level of humidity. If we crawl into a VP liner, then into our sleeping bag we accomplish the following important tasks and results:
  • Maintain 100% humidity --> reduce heat loss through vaporisation
  • Reduce moisture gain in our sleeping bag

Back to the Recommendations:

The Canadian military in researching sleep and clothing systems for usage in arctic conditions did a couple of interesting studies. The studies were looking at deep cold, between 20 and 40 below zero celsius. The following items are useful for us to address at this point
  • Incontinent water loss is 500 -1000ml/night (think evaporative loss not incontinence)
  • Sleeping bags gain an average 15g/hour during usage due to ice buildup in the insulation, or approximately 500g during 24 hours of usage
In cold weather we are unable to produce enough heat to push the vapor through our sleeping bags prior to condensation and crystallization within the insulation. This reduces the insulative quality, increases weight, and overtime can reduce our comfort level. By utilizing a VP, we reduce heat loss, reduce moisture/weight buildup in our sleeping bag and increase our overall comfort. But this still leaves us with the final recommendation: to wear it over a thin insulative layer. Simple, plastic bags against our skin feels really nasty.

From experience, assuming that I am properly outfitted, I have not found a benefit to using a VP until the temperatures begin to dip below -20C. In these conditions I notice a substantial increase in warmth within my sleepingbag and I sleep warmer throughout the night. Upon waking, typically in a baselayer, I will feel slightly clammy due to the 100% humidity conditions that I have been wrapped in for the past few hours. But at these low temperatures, if I wait a few minutes after emerging before fully dressing, I find that the built-up quantities of moisture in the baselayer quickly dissipates.

Being active during these same conditions requires me to think a little differently. My primary concern is venting adequately, releasing metabolic heat and allowing any excess moisture to escape from our body and clothing as quickly as possible. In deep cold (-20C and onwards) my preference is for very permeable, non-waterproof footwear. There is far more risk due to liquid water from within the footwear, than from snow or ice melting in contact with my footwear and leaking inwards. The same can be said of our other clothing layers. In deep cold, breathable rather than waterproof is our primary concern
 
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Andy BB

Full Member
Apr 19, 2010
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Fascinating - many thanks GO.

Actually, it kind of reminds me of some of the things Wiggy rants on about - I'm sure our american cousins are well aware of his somewhat trenchant views on various clothing/insulation issues! For one thing, he doesn't rate goretex and similar at all, saying they just don't work as the thermometer drops. He also goes on about the dangers of ice build-up in down and most artificial fibre bags, again as the thermometer drops. (He also states, quite controversially, that the denser-stuffed a down bag is, the more likely it is to retain moisture and potentially freeze, as the vapour being driven through the bag by the occupant's heat has less chance of reaching the bag's surface.) His solution - and I pray he'll forgive me if I get it totally wrong! - seems to be not to have a densely-woven fabric as the bag's skin, and to have long-strand silicone-coated fibres laminated to the surface of the bag (therefore no quilting and corresponding cold-spots, and a regular separation of fibres). I believe he claims that the silicone coating not only means the moisture cannot enter the fibre strands, but that silicone itself has a slight repelling quality that helps vapour pass through the bag and out onto the outer cover. Here it might well freeze, but this doesn't create any problems, as its on the outside, and not trapped within the bag itself. This ease of vapour transfer means that the occupant will remain dry, and similarly any clothing in the bag will dry out too There are videos on youtube showing someone getting into a soaked wiggys bag in the winter on the flat-bed of a truck, and waking up in the mornng dry...admittedly not below -20C though!

The metabolic issue/skin boundary-layer humidity % issue raised by Grey Owl raises an interesting issue with regard to Wiggy's argument. Presumably the metabolic furnace needed to drive water vapour from the body through the bag (and dry contents and potentially the bag itself) will be substantially more than if one was inside a vapour-impermeable bag, as in the latter case a state of equilibrium would soon be reached. However, unless one was seriously in a life-threatening situation where the availability of food was limited, is that really an issue? I dunno!

The only part of the vapour-impermeable argument I'm not quite getting is the end-result - ie getting up in the morning, and getting out of the VI bag, either wet if not wearing clothes, or wearing damp/wet inner-layer thermals. IN either case, at -20C or lower, how exactly does one dry out and/or warm up? And the other part of that is that you can't dry out socks/boot liners etc by keepig them in the sleeping bag with you overnight. Do you then put on wet clothes?
 

rg598

Native
I think GO covered all the science, some of which I must admit I didn't know.

From a practical stand point, yes, you will have to deal with being wet. You will have to deal with the moisture either way. It will either be on your base layer in the morning, or in your sleeping bag. Either your socks will be wet, or your boots will be wet. As GO said, at low temperatures, your body does not produce sufficient heat to push the moisture out of the fabric before it freezes. Being out for prolonged periods of time in such low temperatures is not a pleasant thing. These are just approaches to minimize the problems.

Again, we are talking about long term stays in cold temperatures. If we are just talking about a weekend trip, or temperatures in the -10C or above range, then there is no need for a VBL. A good place to see the practical application of VBL is Polar Attack by Weber and Malakhov.

I personally an not a big fan of miracle solutions. Some materials may work somewhat better than others, but at the end of the day, we have to deal with the conditions one way or the other. I know all sorts of claims get made by manufacturers, but ultimately, if you look at what people use to climb Rainier, Denali, Everest, and go to the poles, it is just straight forward sleeping bags rates for the appropriate temperature. The rest comes down to common sense and good technique.