Waterproof inside layer for winter bag

[rOg w]

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[Woubeir (from Europe)]

I know pf some people who even use a VBL when it's outside 50°F but very humid. They claim it's the only thing that effectively prevents moisture accumulation inside their bag. Freezing is definitely not a problem here.

[Dave @ Oware]

I have used a VBL jacket and bag liner at the same time so I could wear a down jacket inside my VBL bag liner. Worked well. Wore the VBL jacket when skiing in sub-freezing temps over a poly shirt.

Camp 7 used to offer a 3 bag system of VBL, down bag, polarguard overbag that I really liked.

On Denali, people have used and inner down bag that had waterproof inner shell. The also have used a vest that had a neoprene back, breathable front to keep sweat from forming against the pack and inside insulating layers.

[Woubeir (from Europe)]

@David
What kind of liner ?

[Jacob D]

Lots of good points in this thread. This stuff seems to get re-hashed fairly often. Depending on preference either VB clothing or a synthetic top quilt with breathable inside shell would probably be the best two options.

I haven't stayed on top of the discussion/subject of the synthetic top quilt here on BPL but I know a few people who do it and for the kind of trips they do (not lengthy winter expeditions) it seems to be a pretty good solution. I'm talking about supplementing a down bag with a light synthetic quilt for those who haven't run across this before. Idea being to try and move the zone where vapor condenses from the down bag into the synthetic top quilt. This also has the benefit of mitigating the effect of spindrift getting on you overnight. Seems to work fairly decently.

VB clothing is in my mind the best way. I don't have a true VB clothing system so I just use my rain gear layered over a light wool base layer. I can then add a down jacket and/or down pants over the rain gear (if I need to). This works great for me because it's generally how I like to move around in the winter anyway, and when in camp the down layers can just go right on over everything. I don't do long trips in the snow but has been a good setup for shorter multi day trips.

Skurka has a good article about VBL. I thought it was worth the time it took me to read it.

http://andrewskurka.com/2011/vapor-barrier-liners-theory-application/

Now if only we can get some snow. California feels like spring right now… not good.

Jacob.

[Jerry Adams]

From Skurka article:

"VBL’s are optimal for just a narrow range of conditions—namely, multi-day outings in frigid temperatures"

[BPLwiia]

"I haven't stayed on top of the discussion/subject of the synthetic top quilt here on BPL but I know a few people who do it and for the kind of trips they do (not lengthy winter expeditions) it seems to be a pretty good solution. I'm talking about supplementing a down bag with a light synthetic quilt for those who haven't run across this before. Idea being to try and move the zone where vapor condenses from the down bag into the synthetic top quilt. This also has the benefit of mitigating the effect of spindrift getting on you overnight. Seems to work fairly decently."

That makes sense and is a simple solution.

[Matt Dirksen]

+1 on the double bag method.

This whole vapor barrier thing just doesn't seem right to me.

In the residential building world, interior vapor barriers are becoming a thing of the past in climates south of Canada. The reason why this is has recently changed in the building world is due to the fact that there are too many failures involved with wall systems not being able to properly dry out, especially in areas where the vapor barrier has been compromised. Although the "building science" is finally catching up, there is still a lot of controversy out there, leading to mold & rot inside of people's walls.

(here's a good conversation on it: http://www.buildingscience.com/conversations/conversation-vapor-barriers)

Because of what I am watching unfold in my own profession, I am VERY skeptical of vapor barriers in general.

In a sleeping system, if one has the ability to "warm the envelope" (and move the dewpoint outside of the primary insulation), I'd bet the sleeper will be much more comfortable (and sleep better) in the long run. Furthermore, there much more surface area of materials for moisture to distribute itself, making drying much easier.

Like in buildings, there is likely too great a risk for "holes" to form in a vapor barrier system, exacerbating convection risk. If you have condensed moisture against your skin and you switch between back and side sleeping, what's the chance of a little bit of air to seep down into your system and instantly rob you of all that moist heat? Even if you were sleeping in a drysuit, the ambient moisture just within the air envelope between your drysuit and that first layer of insulation would run a risk of hitting the dew point inside of that bag.

People move while they sleep. At least if you move around wearing a wicking base layer and a inner bag, the risk of convective heat loss is likely minimized.

But there are those that swear by the practice of using VBL's, and somehow they've mastered the techniques needed to make it work for them. It just seems safer to me to bring the extra 50degree outer bag that can "catch" that condensing moisture.

The problem with empirically testing any of this is we all have different tolerances of "comfort", and probably all move about differently while we sleep. Not to mention the temperature and RH of any place we test in would likely vary.

Either way, I doubt the traditional Inuit used VBL's. But who knows…

Matt

[Tom Lyons]

They key to avoiding the heavy sweat inside the VBL is to regulate your temperature to neutral. If you are overheated and sweating inside the VBL, of course it's going to be wet inside. The idea is to keep a neutral temperature, by regulating your insulation.
This is what most neophyte VBL users fail to think about regarding VBL.

[Rick M]

del

[Matt Dirksen]

How does one regulate temperature while supposedly being asleep?

(I guess that's my inner skeptic!)

;>D

[Anonymous]

I use to be somewhat skeptical of VBL in general. I've come to consider that they have their place as a niche piece of gear for certain conditions. Particularly bitter cold and being out longer. Too many people have reported that they help a lot in those conditions.

I'm still skeptical of the active use of VBL's, ala Skurka's reports for example. Having used VBL in stationary/rest conditions, i could only imagine the difficulty in regulating it during physical exertion. I mean, i understand the point, but i prefer breathability verse being able to wear a lightish down jacket. In that case, i would rather not save weight, but instead save comfort.

Meanwhile your baselayer is constantly soaked, no matter how well you try to regulate it.

When you're sleeping and your metabolism goes way down, i think the main regulation you really have to do, is to not have a bag or quilt that is too warm for the conditions. Figure the VBL will add at least 5 degrees of warmth to your sleep system.

Personally i would not use one, since some of my past experiences with same, until it gets down to around 15*F or so. Around low to mid 20's, was a bit clammy at first, which i didn't like the feeling of. My body did seem to adjust though, and when i woke up, the clamminess had gone down. Some say one's body does adjust accordingly some to the sensing of perspiration on skin. I'm not sure, it was either that, or just that my metabolism had gone down some more notches by that point.

Matt, just curious, have you experimented with using VBL's?

[Jerry Adams]

To regulate temperature while sleeping

Lower quilt a little, take hat off, loosen any cover around neck

If you get cold, start putting stuff back on. Maybe add a warmer hat or balaclava.

Or you could take off your vest or jacket that you wear inside sleeping bag and set it where it's handy, and if you get cold, put it back on.

[Dave @ Oware]

"How does one regulate temperature while supposedly being asleep?

(I guess that's my inner skeptic!) "

The same way you do at home in your bed. You pull the covers down a bit, or stick you foot or butt out for awhile if your system allows.

On a multiday ski trip in sub-zero temps with winds and using a floorless shelter I have been know to wear
polypro
vbl jacket (homemade)
down jacket
vbl bag liner (homemade)
2 lb summer down bag
2 lb summer polarguard overbag
waterproof bivy (homemade)

worked great, no moisture buildup that I could tell and the bags were as warm at the end of the trip as the beginning, unlike
the subzero synthetic bags we used before.

[Woubeir (from Europe)]

@Matt
I am a licenced energyconsultant for the building industry and as such I understand very well what you mean. An added insulation layer to catch the condensation is indeed better. However, in contrast to insulations used in the building industry, we're talking here about down and its properties. And sometimes that can mean a VBL of some sorts does work in some situations.

"I'm still skeptical of the active use of VBL's, ala Skurka's reports for example."
Remembering that Beck Weathers told in his book how he used VBclothing while climbing Denali and it made him very dehydrated, I'm also a sceptic.

[Jerry Adams]

That doesn't make sense that VBL would make you dehydrated, because it reduces sweating.

You don't need very much insulation to keep you warm while exercising, so therefore VBL is less useful? Hard to keep from sweating?

[Author]

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