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Waterproof inside layer for winter bag
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just Justin Whitson
(ArcturusBear)
Re: @jerry on 01/27/2014 22:45:31 MST Print View

Janos, it would be well under 32 degrees F i think. But i think you're generally correct in that the colder it gets, the less humidity tends to be in air. Ime when its below 20* F or so, tends to start feeling much dryer (but this inland and away from larger bodies of water).

Certain conditions, might strongly change that tendency though, like being near large bodies of water?

Woubeir (from Europe)
(Woubeir) - F - MLife
Re: Re: @jerry on 01/28/2014 04:31:28 MST Print View

AFAI can remember, the colder it gets, the lower the absolute humidity necessary to reach a certain RH (so also lower then freezing), but also less moisture is needed for condensation to occur e.g. at 32 °F air can contain max. 3,77 g. moisture/kg. air but at 0 °F it's only about 0,7 g.max..

Edited by Woubeir on 01/28/2014 04:41:44 MST.

Ike Jutkowitz
(Ike) - M

Locale: Central Michigan
Re: on 01/28/2014 06:23:11 MST Print View

"Ike, i wonder if this would be a case wherein lower quality down, especially if over stuffed, might work noticeably better than the super high quality and super downy stuff like you currently have?"

I've been thinking a lot about that lately. Never used to think about condensation at all with my trusty old WM puma, other than to shake the ice crystals off the shell each morning. In comparison, with the high performance 900 fill, I figuratively walk on eggshells trying to keep moisture out. VBL suit, synth overquilt, and every effort to avoid dampness near it. I still notice loss of loft the first night out.

For extended trips in extreme cold, I'll still take the old bag despite a nearly two lb difference. It is worth it just for simplicity's sake

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: @jerry on 01/28/2014 08:27:27 MST Print View

I don't think RH has much to do with it

Picture worth 1000 words:

temp gradient

The "22 F Air Temp" line shows the temperature gradient from skin (92 F) to ambient (22 F). This includes the boundary layer of air surrounding the sleeping bag that drops the temperature about 10 F. The point where the temperature reaches 32 F is right at the outside edge of sleeping bag.

The "0 F Air Temp" line shows it for 0 F outside air temp.

Water vapor is sweated from your body and goes through sleeping bag to the outside.

For the 0 F case, the water vapor reaches 32 F inside the sleeping bag. At that point it will freeze. Water (frozen) will accumulate inside the sleeping bag.

For the 22 F case, the water vapor reaches 32 F just outside sleeping bag, so it will exit sleeping bag, no water accumulation.

So, if the air temperature is above about 22 F, you don't have to worry about VBL.

For temperatures below 22 F, VBL starts being more useful to prevent water accumulation inside bag.

This is more theory based, as I avoid temperatures below 22 F. Starts being too difficult keeping drinking water from freezing. I suspect 99% of backpackers also avoid the really cold temperatures for many days.

On the Stephenson website, he talks about arctic expedition. Temperatures much below 22 F. Many days for water to accumulate. That's when a VBL is really useful.

For you 1% that go on arctic expeditions (or Minnesota right now) VBL is really useful, otherwise it's not.

Daryl and Daryl
(lyrad1) - MLife

Locale: Pacific Northwest, USA, Earth
Re: Re: @jerry on 01/28/2014 09:53:39 MST Print View

Jerry,

Nice summary.

Your chart helps me understand why I usually get so little condensation inside my very small, all fabric inner tents. The air inside the inner tent stays warm enough to maintain its vapor state until it exits the inner tent and comes into contact with the fly.....at which point it is shocked into wetting itself.

rOg w
(rOg_w) - F

Locale: rogwilmers.wordpress
deleted on 01/28/2014 10:44:00 MST Print View

deleted

Edited by rOg_w on 02/05/2014 20:48:45 MST.

Woubeir (from Europe)
(Woubeir) - F - MLife
Re: Waterproof inside layer for winter bag on 01/28/2014 11:10:10 MST Print View

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.

David Olsen
(bivysack.com) - F - M

Locale: Channeled Scablands
Re: Waterproof inside layer for winter bag on 01/28/2014 12:40:25 MST Print View

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)
(Woubeir) - F - MLife
Re: Re: Waterproof inside layer for winter bag on 01/28/2014 13:26:26 MST Print View

@David
What kind of liner ?

Jacob D
(JacobD) - F

Locale: North Bay
Re: Re: Waterproof inside layer for winter bag on 01/28/2014 15:38:47 MST Print View

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
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Waterproof inside layer for winter bag on 01/28/2014 16:31:27 MST Print View

From Skurka article:

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

wiiawiwb wiiawiwb
(wiiawiwb) - F
Top synthetic quilt on 01/29/2014 05:27:27 MST Print View

"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
(NamelessWay) - MLife

Locale: Mid Atlantic
Re: Top synthetic quilt on 01/29/2014 15:21:39 MST Print View

+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
(towaly) - F

Locale: Smoky Mtns.
maintain neutral temp on 01/29/2014 17:41:21 MST Print View

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
(rmjapan) - F

Locale: London, UK
Re: maintain neutral temp on 01/29/2014 18:00:55 MST Print View

Good point. We sometimes seem to forget the Winter maxim that "if you are sweating, you are doing something wrong."

Matt Dirksen
(NamelessWay) - MLife

Locale: Mid Atlantic
Re: maintain neutral temp on 01/29/2014 18:32:44 MST Print View

How does one regulate temperature while supposedly being asleep?

(I guess that's my inner skeptic!)

;>D

just Justin Whitson
(ArcturusBear)
Re: Re: maintain neutral temp on 01/29/2014 20:16:24 MST Print View

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
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: maintain neutral temp on 01/29/2014 21:25:06 MST Print View

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.

David Olsen
(bivysack.com) - F - M

Locale: Channeled Scablands
Re: Re: maintain neutral temp on 01/29/2014 22:03:51 MST Print View

"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)
(Woubeir) - F - MLife
Re: Top synthetic quilt vs VBL on 01/30/2014 05:30:07 MST Print View

@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.