Vapor Barrier question

[Lynn Tramper]

>it is a semi "vapor barrier" for slowing evaporative cooling rather than completely halting it while still maintaining breathability.

That just sounds like any old WPB clothing would do. But not a windshirt!

[Brad Groves]

FWIW, my trips are in the quite humid Great Lakes region. I have found the VBL to be invaluable here, and a significant contribution to my kit. Of course, if you're on a winter trip then humidity will generally be lower, anyway…

[Michael Cheifetz]

Eric,
how often will you use that?

i guess if you are like me and the answer is not often and you only want this for protecting your bag on multiday cold/wet trips then getting a full blown VBL is costly and heavy….
from my understanding (NOT PERSONAL EXPERIENCE) people who regularly do multiday hikes in subfreezing wet conditions will definitely need VP clothing and/or liner – but for usage that is shorter i see no reason not to try garbage/garden bags.
Another option (i saw a guy in the UK with this) might be a cuben fiber VBL – very very lightweight. if your a DIY guy u can do yourself or get some of the cottage guys to do for you.
M

[Mary D]

Praveen, I have the Brawny Gear rainsuit. One of the reasons I got it was to have the vapor barrier possibility as well as rain gear. This use was suggested on Brawny's website, http://www.trailquest.net/ultralight.html#Clothing . I used it last summer on below-freezing nights in the Wind Rivers, worn over my base layer (Capilene) and a fleece balaclava. It worked just great! I was quite comfortable, and there was no condensation in my bag.

You could also make your own silnylon VBL bag or clothing for a better fit.

I was using a 20* WM bag. I got a little cold the two nights my dog's water dish froze completely solid, but cinching up the draft collar tighter seemed to do the job. At least one of those nights, my insulated air mattress (POE) was rather borderline, too. I have since used a piece of 1/8" Gossamer Gear Thinlite pad, cut to torso length, on top of the mattress for cold nights. I've also started taking a thermometer. I am, obviously, a very cold sleeper!

[Eric Blumensaadt]

Get some ripstop, urethane coated, aluminized nylon fabric from SEATTLE FABRICS or other outdoor fabric shops and make your own VBL. It will be as good but MUCH less expensive than commercial fabric VBLs.

Once you've sewn it up seal all the (French)seams on both sides and you are in business. Try to use French seams for ease of sealing, with the exception of the top opening drawstring tunnel.

Eric

[James Dubendorf]

With all the great minds at work on this site, I am sure to be reinventing the wheel to some degree, but here goes:

In some very preliminary experimentation with a system of vapor barrier liner (at this point, simply a few garbage bags duct taped end to end), down sleeping bag, and mld soul bivy, I can attest to the fact that the garbage bags are an effective vapor barrier (I know I am not exactly breaking new ground with this claim!). However, in practice, I have found that it is difficult to simultaneously regulate body temperature through adjustment of insulation and maintain the vapor barrier "seal." I'll operate on the assumption that an effective vb system requires both regulation of insulation and an effective seal in order to create that vb "microclimate."

If the liner tightens around the neck/shoulders/face, any use of the hands or arms outside the liner requires a breaking of the vb seal. I like to have my arms available to adjust headwear or other insulating components in the sleeping bag, move my pillow, check the time and temperature, grab a drink, etc. and so this arrangement is quite inconvenient for me. Also, while I do not feel claustrophobic in a bivy, the liner over or around the head feels a little too close. Obviously, vb clothing solves this particular issue, and allows for more convenient use of insulated clothing in the sleep system. However, I am new to the vb game and own no vb clothing. I would like, therefore, to experiment with a compromise system that 1) incorporates insulating clothing more easily than a full vb liner, 2) allows, like vb clothing, for free arms and hands while asleep, and 3) provides many of the benefits of either a full vb liner or vb clothing.

The plan is for a 3/4 length vb liner that cinches beneath the armpits with a piece of elastic (if experimenting with garbage bags, simply fold the top of the bag over and tape shut to create a channel for the elastic). Underneath this liner is worn the typical base layer top and bottom- I will be experimenting with merino wool. With this liner in place, one retains use of their arms. Furthermore, top layers may be worn OVER the base layer and liner, and items placed between the liner and bag, or the bag and the bivy, are much more easily adjusted. In theory, the liner still blocks much moisture that would otherwise enter the insulation, and much of the body benefits from the vb. Furthermore, the areas not protected by the liner around the shoulders are head are more easily vented (being at the open end of the bivy), and overall there is less insulation to dry out.

My expectation is that very little moisture would travel deep into the insulation from shoulders to feet. Furthermore, having head, arms, and shoulders outside of the liner might assist the crucial regulation of temperature not only by allowing for easier manipulation of insulating components, but also by providing options for heat dissipation outside of the vb liner which, according to this post by Craig Tenney at

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=1793

are essential to an effective use of the vb concept.

The liner itself could also be used as a pack liner, or even as a piece to pull over shoes and legs during rest breaks if needed. Depending on conditions, one might even be able to dry out gear by putting it between the liner and bag, or between the bag and bivy, down towards the feet.

Any thoughts?

[Jim W.]

Someone asked about a "semi vapor barrier liner". In my opinion that's the worst of both worlds. When you're cold and barely sweating then it wouldn't block transpiration. It would still mostly block air movement which is probably a major factor in the effectiveness of VBL's. When you get a bit hot though, and start to sweat a bit then it would act to block some of the transpiration and you would probably be just as hot as when you overheat in a true VBL.

I have a synthetic fill liner bag that includes a "Silver Lining" reflective layer. In fact this layer is basically a mylar space blanket with small perforations to let moisture out. Unfortunately it doesn't do so very well and has the narrowest comfort range of any sleep system I've ever used. At 55F it's hot and steamy, 50F it's comfortable, and below 45F it's getting cold. Lack of a zipper doesn't help. On the other hand my VBL is great. I don't use it in warm weather, use it to my armpits as weather gets cooler, then up around my neck when it's cold.

[David Olsen]

A full length vbl can be very flexible used either full length
when it is not too cold to keep moisture out of your
sleeping bag, or pushed down under your arm pits 3/4 style so you can wear
insulated top layers normally with the vbl underneath the
clothes. Then any extra jacket or vest, you may have can be
pulled over the feet and legs OVER the vbl so they stay dry
too.

Like many things, people get too hung up on things working
perfectly as the theory suggests.
Sealing seams will not likely gain you
anything on a VBL. The amount of moist air that could get through a seam would be minimal. Your breath gives off the
most moisture and you don't want to try breathing in a
VBL liner.

Even a goretex parka will add warmth in
your sleeping system if you need a little extra. Wear it
inside for more dead air spaces or pull it over your feet
on the outside like a half bivy depending on which part
of you gets cold first.

One thing I like about VBL's is they let me know early
when I am overheating to the point of sweating and wake
me so I can adjust my layers. Otherwise all my
layers end up drenched before I realize I am wet.

Old school sleeping naked worked so well because you could
easily adjust your one layer for more or less warmth just
by pushing around part of your sleeping bag or quilt. Warm
air easily traveled from your core to your extremities.
People who get cold feet easily, should stick with full
length sleeping layers that let warm air circulate, not
trap it next to your core with lots of clothing, VBL
or not.

[James Dubendorf]

David,

Thank you for your input. It is certainly true that a full length vb liner can easily be arranged under the armpits as opposed to full length, something I probably should have experimented with more in the course of things! I suppose potential advantages with a liner designed to 3/4 length would be a very slight savings in weight, more flexibility to do double duty as a pack liner (due to less excess material), and less excess material to deal with while in the liner, bag, bivy, etc. Perhaps this 3/4 liner could be employed when one anticipates temperatures towards the warmer end of the spectrum where vb becomes less effective?

My own concern about the "seal" is not so much with the seams of the liner, but with the seal between the liner and the body at the top of the bag. I am still new to vb technology, and so I have not yet figured out whether my issues of comfort have to do simply with more effective regulation of insulation, or with more effective maintenance of that seal- which, when maintained, by some accounts creates the important microclimate around the body. Of course, I may be overestimating the importance of this seal. You can probably tell that these are vb liner "baby steps," as I am very new to this game. Also, I am working within the constraints of available gear, expense, and limited fabricating skills (I can duct tape plastic bags just fine!).

[Roger Caffin]

Hi James

You need to ask yourself exactly what it is you are trying to achieve. I don't think this question has been answered yet.

If you are trying to keep your sleeping bag dry and fully functional, then clearly having the VBL extend right out of the SB is the only solution. This is the normal use for a VBL: Let it look after the moisture and let your dry SB look after the warmth. Plastic bags work fine, as long as they don't rip. Silnylon will last longer.

If you are trying to use it as a warmth layer, then that is far more tricky and requires a lot more experience. It is also far more dependent on the exact circumstances each night.

I suggest focusing on the first use of the VBL. Get some experience there in cold weather first.

Cheers

[James Dubendorf]

Roger,

I've benefited a great deal from your contributions to BPL, and would like to thank you for your time and consideration. I see now that my plan is a bit schizophrenic. If I understand you correctly, moisture management within the SB and the insulative properties of the system are two related but nonetheless separate functions of the vb. Perhaps in the service of comfort I am cutting corners- rather than abandon the full length liner, perhaps I should put more testing hours in before seeking alternatives. Admittedly, the testing I've conducted has been in cold but not frigid conditions (not much below 20 F), and it has been tricky to avoid moisture, clamminess, and a bit of interesting smell thrown in. Longterm winter travel is not yet part of my repertoire, and sunny drying days in the Rockies are often plentiful, but I enjoy testing new approaches, and I would rather not wait until I rely on this system, or the sunshine, for my safety to try it out!

My primary interest at this point with the vb liner is moisture management, as I now own down SBs and would like to learn how to extend their application as much as possible before pursuing (and INVESTING in) other options, such as synthetic insulation. I am aware that you use down over long trips within a double wall tent system. As I've noted above, my broader interest is in fitting the vb liner into a system of liner/SB/breathable bivy- kind of a Skurka lite approach without the vb clothing and duct tape on the nose! I would not feel comfortable relying on the potential insulative properties of the liner, and am happy on "testing" trips to carry extra weight in the service of science (ha).

[Roger Caffin]

Hi James

> moisture management within the SB and the insulative properties of the system are
> two related but nonetheless separate functions of the vb.
You got it!

> perhaps I should put more testing hours in
Oh yeah – lots more winter trips! They are essential 'in the service of science ' as you put it. A most excellent justification for more trips – if one ever needed excuses!

It certainly would be interesting to hear from you how the garbage bags go. How well do they last in the field? Lots of interest there.

Get walking…
Cheers

[James Dubendorf]

Roger,

Far be it for me to shirk the clarion call of science and impede the struggle for knowledge, even if it does require me to defer all those responsibilities and head to the hills. News to follow once the opportunity to go play in the snow, ahem, conduct vital research, presents itself.

James

[Roger Caffin]

Sorry Dear, I have to go up the mountains this weekend to test this new Vapour Barrier Liner for BPL: they are waiting on the results of this vital research.

Hum ….
:-)

[Lynn Tramper]

>Sorry Dear, I have to go up the mountains this weekend to test this new Vapour Barrier Liner for BPL: they are waiting on the results of this vital research.

The response: Great! Can I come too?

I am a converted fan of VBL clothing as opposed to just a sack. The ability to wear all my insulative clothing over my VBL is essential to my sleep 'system'. They also make great wind gear if you're just standing around and not exerting much effort.

[Sharon Bingham]

I was interested in the semi-barrier concept mentioned earlier.

It seems like you should be able to get double-duty out of UL rain gear items (say something like the GoLite Virga jacket and Reed pant), if you used them in place of true VB clothing.

The advantages I'd see to something like this are: 1) you may already own this type of gear and 2) you're likely to be carrying it with you anyway.

If you're primarily looking to prevent moisture from entering your SB from sweating, and/or trying to gain a few extra degrees of warmth to extend the bag's comfort range, it seems like using your WB rain gear could be a reasonable compromise.

While I understand that WB material is not a full VB, it certainly allows less vapor to pass through than using nothing. And we all know that WB still doesn't allow much vapor to pass – if it was THAT breathable, it'd be fine to use as the exterior fabric of the SB itself (which most people agree that it is not)…

So surely, for the casual/occasional low-temp use, say in a situation where you're only going to be spending a few nights in sub 32F temps, it would be better than nothing at all, while still not requiring an additional investment, or carrying the extra weight of a VB SB liner, or dedicated VB clothing?

[Lynn Tramper]

Unlikely to work except as a bit of extra warmth. WBP bag covers don't work well because they are too far from your body's heat to let vapour through, especailly on a cold night. If you wear your raingear close to your skin (as a pseudo-VBL), then the vapour transfer will be quite high. If you wear your raingear as an outer layer, then you inner insulation may get damp. This is because WPB fabric works via a temperature gradient. If your perspiration cools too much before it hits the fabric, then you get condensation. If you wear it next to your skin inside a warm sleep system, condensation will happen to a much lesser extent, unless you are literally freezing to death.

[Sumi Lavin]

I want to disagree that wb sleeping bags do not work very well. Have you been in a situation where the cover caused the insulation to fail?

[Lynn Tramper]

>I want to disagree that wb sleeping bags do not work very well. Have you been in a situation where the cover caused the insulation to fail?

Yup. Yellowstone, midwinter temps in the -40s at night. Took only three days to force us into a hotel due to down collapse from interior moisture.

I sold the bag after that, and have not tried WPB bags again. Have slept in similar conditions since then without too much problem.

[Sumi Lavin]

Can you share what year it was and the bag model? Perhaps tent you were in?

[Lynn Tramper]

You wouldn't be familiar with either the tent brand or the bag brand. The tent was a 'baffled' double wall tunnel tent (think of a sleeping bag without the down fill). The baffling made it too warm to use other than winter trips. The bag was a 2kg bag rated to minus 20C, and covered with GoreTex Dry Loft. The year??? No idea. I don't keep track of such things.

In similar conditions since then, I HAVE seen condensation inside my Epic covered bivy bag, but it didn't cause a problem because I could easily remove the bivy and pack it separately.

[Sumi Lavin]

How experienced were you at the time? Maybe you had your head inside the bag for 3 nights, breathing moisture into it? That's a lot of bag to lose in 3 nights. I asked about the year because the older Goretex dryloft was less breathable.

[Lynn Tramper]

I was very experienced (even when 'inexperienced I knew better than to breathe into a bag). As for breathability, that has not been the issue with the Epic bivy bag in similar conditions. Epic is far breathable than any WPB fabric available, yet, in cold enough conditions, vapour has managed to condense before it gets to the outer fabric. That is the main issue IMHO.

And it doesn't take a 'lot of loft' loss from a minus 20 bag when you are trying to sleep at minus 40. The bag was clearly damp and listless. I would guesstimate the loft was around 25% less than when fully dry, but I did not measure it (too cold to think about such details).

[David Ure]

Interesting. I find eVent more breathable than Epic in all conditions and truly waterproof, which Epic isn't.

As far as down collapse, are you saying that you had zero opportunity to pull out your sleeping bag at some point during the day to dry?

Edit: -40….okay, understood.

[James Dubendorf]

Hello All,

It would seem that the functionality of vb clothing or liner is equally relevant in cold temperatures regardless of the outer material of the SB. A vb in this situation is employed to handle interior rather than exterior moisture, and this moisture in very cold conditions would end up in down regardless of the outer material of the SB, because that this point the relevant variables are temperature and dewpoint, where condensation has been moved inside the down in cold temperatures. I've only used SBs with breathable fabrics and maybe a DWR, and employ a lightweight non-waterproof bivy to deal with exterior moisture (and other benefits). If I don't need the bivy, I can use my SB with vb items and w/o bivy and things become even quicker to dry. One potential advantage of this setup is that when presented with an opportunity to dry out the SB, the SB comes out of the bivy and dries quicker than a similar bag with less breathable fabric. Also, I've been in situations where condensation forms as frost on the inside of the bivy- this can simply be brushed off in the morning, and usually does not appear to influence the SB at all. With a wp/b shelled SB, this would not be possible.

If those who enjoy SBs with a wp/b shell have had different experiences, it would be great to hear them- in what conditions did they excel? down or synthetic? etc.

[Author]

Posts