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#122643 - 10/19/09 08:01 PM Vapor Barrier Liner for sleeping bags (VBL)
Jim M Offline
member

Registered: 11/23/03
Posts: 366
Loc: Kitsap Peninsula, WA
I have had some lengthy discussions about this with friends and done some reading on the subject as well. What I found out is that the claim that "Sensible Sweat" stops under certain conditions (as Stephenson says) of temperature or humidity is simply wrong. There are lots of well documented articles (search "Google-Scholar") on the subject of sensible sweat. None suggest it ever stops. Yet, some, not all, who try a VBL are able to sleep without accumulating condensation. So here is my question. Where does the water vapor go if it doesn't condense on the VBL?
_________________________
Jim M

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#122650 - 10/19/09 09:17 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: Jim M]
DJ2 Offline
member

Registered: 01/06/02
Posts: 1348
Loc: Seattle, WA
I'm guessing here but I like this sort of question.

Without the vapor barrier it must just pass through the bag into the air. To test this I've weighed my bag at night and in the morning and found no measureable weight change.

With the vapor barrier (if it doesn't collect on the vbl) then it must be on the person and/or their sleeping clothes or it must have escaped through the head (open) end of the sleeping bag (and liner).

From a practical matter I've had no trouble finding the moisture when I've experimented with vbls. It is all over me and the inside of the vbl. I've tried it twice and never made it through the night without getting so wet that I aborted the mission.

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#122659 - 10/19/09 10:07 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: DJ2]
OregonMouse Offline
member

Registered: 02/03/06
Posts: 6765
Loc: Gateway to Columbia Gorge
Just to show how different individuals can be, I always use vapor barrier clothing in my sleeping bag when it's below freezing. I have non-breathable rain gear and wear it over a base layer. If it's really cold (like my recent 18*F night) and I need more wraps, I put them on over the rain jacket so they won't get damp.

The theory is that once the humidity inside the vapor barrier gets high enough, your body stops producing moisture so you stay in equilibrium. It does work for me, and keeps my sleeping bag a lot drier. Without the vapor barrier, the moisture from my body condenses (and freezes) on the underside of the outer shell (I could feel it there!). A couple of nights of that can really reduce the effectiveness of your bag. Remember, though, this is for well-below-freezing conditions, not for the low 30's or higher.

I wouldn't ever want to try a vapor barrier when I'm active, though, which is where I part company with the Stephenson folks. I try really hard not to sweat when I'm active in cold weather.
_________________________
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey

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#122661 - 10/19/09 10:42 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: OregonMouse]
DJ2 Offline
member

Registered: 01/06/02
Posts: 1348
Loc: Seattle, WA
Viva la difference ( I have no idea how to spell, or say for that matter, this phrase).

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#122665 - 10/19/09 11:07 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: Jim M]
Heber Offline
member

Registered: 12/31/07
Posts: 245
Loc: St. Louis, Missouri
I'm not sure about stopping insensible sweating (I think the correct term is "insensible" rather than "sensible" sweating) with a VBL. However it may not make a lot of difference whether it stops or not. What's more important is stopping it from evaporating. That cools you a lot. If you can just keep that moisture in a liquid state you will stay quite a bit warmer. That's what a vapor barrier does.

Now whether you can sleep with that clammy feeling is another question. I can sleep with VB socks on but that's about it. Some can't do that.

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#122670 - 10/20/09 12:06 AM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: Heber]
phat Offline
Moderator

Registered: 06/24/07
Posts: 4107
Loc: Alberta, Canada

Not sure I believe the sensible sweat thing, but I believe the frost in the bag at subzero temps. I wish I could sleep in a vbl but can't stand it. my solution has been to use a synthetic outerbag so the frost layer stays in that instead of my down at very cold temps (or have a wood heater in my tent)

I know enough people who use vbl to know it does work. the moisture stays in you or goes out through the top.

_________________________
Any fool can be uncomfortable...
My 3 season gear list
Winter list.
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#122689 - 10/20/09 11:02 AM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: Jim M]
Roocketman Offline
member

Registered: 03/10/07
Posts: 203
Originally Posted By Pliny
I have had some lengthy discussions about this with friends and done some reading on the subject as well. What I found out is that the claim that "Sensible Sweat" stops under certain conditions (as Stephenson says) of temperature or humidity is simply wrong. There are lots of well documented articles (search "Google-Scholar") on the subject of sensible sweat. None suggest it ever stops. Yet, some, not all, who try a VBL are able to sleep without accumulating condensation. So here is my question. Where does the water vapor go if it doesn't condense on the VBL?


OK, your logic could not be logical.

Sensible and insensible sweat are involved, and maybe they are confused. I dunno without seeing what you read.

Evidence strongly suggests that some people get along well with a VBL, and some don't. So, maybe not everybody is the same. Important point.

The people who don't get along well with VBL complain of being wet or uncomfortable.

The people who get along well with VBL don't have that complaint.

Maybe those who get along well with VBL are those whose insensible sewating shuts down, as advertised by the VBL theory. In that case, the question of "where does the sweat go?" has no meaning.

Keep an open mind, and thimk. :-)

I find that my hands sweat a lot, and for winter bicycling, the only type of gloves that don't fill up with sweat for me are breathable -- no waterproof/breathable glove breathe enough for me. This is also true of the owner of the local bicycle shop. He tries to caution his staff not to oversell the multitude of waterproof breathable gloves in stock. Both of us use a fairly dense fleece glove which is somewhat wind resistant but stays dry and is warm. There are dense wool gloves that might work well too.

I have a good sized sack of worthless, for me, waterproof/breathable gloves.

I am not a likely candidate for a VBL approach. I"ve tried it with gloves, and while the glove will stay dry, the wetness of my hands is too much of a bother.

Other people, obviously, don't respond in the same way.

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#122695 - 10/20/09 12:49 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: Roocketman]
ringtail Offline
member

Registered: 08/22/02
Posts: 2296
Loc: Colorado Rockies
Good post rocketman. That may be the answer. I can semi use vapor barrier clothes. It works for me as long as I adjust my insulation for changes in metabolism. I generally take a longish walk to go to the bathroom and then need to layer down until my metabolism returns to the resting state. In the morning when my body temperature normally starts to rise I need to layer down to avoid the clammy feeling.

It is amazing how we can train our bodies. I drink two glasses of water before I exercise in the morning. The other day I was going to go for a walk after a football game so I drank two glasses - the game went into overtime, but I started to sweat anyhow. Nice to confirm Pavlov.
_________________________
"In theory, theory and practice are the same. In practice, they are not."
Yogi Berra

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#122699 - 10/20/09 02:21 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: Roocketman]
Trailrunner Offline
member

Registered: 01/05/02
Posts: 1835
Loc: Los Angeles
I have experimented with a simple silnylon VBL my wife made for me. Sometimes it works, sometimes it doesn't. By "works" I mean I probably would not be as warm without it, and I wake up with reasonable but not excessive dampness. I don't use it above freezing.
_________________________
If you only travel on sunny days you will never reach your destination.*

* May not apply at certain latitudes in Canada and elsewhere.

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#122704 - 10/20/09 05:01 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: Trailrunner]
OregonMouse Offline
member

Registered: 02/03/06
Posts: 6765
Loc: Gateway to Columbia Gorge
I think Trailrunner has it--you're going to have to experiment to see if a VBL works for you. It does for me, but obviously not for everyone--we're all different!

A few one-night trips into frigid areas would be a good test--preferably close enough to your car that you can bail out if things go awry. I normally recommend the back yard (if you have one) as the ultimate gear testing location, but in your case, as in mine, it usually doesn't get cold enough!
_________________________
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey

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#122706 - 10/20/09 05:06 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: ringtail]
Roocketman Offline
member

Registered: 03/10/07
Posts: 203
From "The Outward Bound Staying Warm in the Outdoors Handbook" by Glenn Randall.


Page 14

... " When I first bought a VB shirt I put it on next to my skin, added one thin layer on top and went for a bike ride on a windy, 40 degree day. To my astonishment, I was simply too hot. For active sports, I'd recommend VB clothing only for temperatures below freezing. It really comes into its own on days when unprotected water bottles freeze solid before noon - days when the high might be zero and the low 20 or 30 below. For inactive sports, some people recommend its use in temperatures below 65. Personally, I do quite well with conventional clothing down into the 20's, even when I'm inactive. ..."

On page 16 he discusses:
Vapor Barrier Sleeping Bag Liners

He states that VB liners let most people sleep comfortably in temps 10 to 15 degrees colder than they could tolerate in just the bag. A VB liner is particularly useful with down to keep loft loss from happening when the down gets wet from perspiration. He usually leaves his VB liner open at the neck to allow some moisture to escape from the clothes. And on a long trip, take every opportunity to dry your sleeping bag.

In his discussion on socks, he discusses Hyperhidrosis or excessive sweating of the hands and feet and these people find that their feet get so wet so quickly that VB socks do more harm than good. About 10% of folks have this.

If you are a naturally sweaty guy, this may not be your cup of tea, or bowl of sweat.

Be sure to read the good stuff on VB which balances fantastic claims with some realism.

Unlike some Hanger Bangers who excessively trumpet the wonders of their hangup, you need balance in the discussion of something like VB. Otherwise you can end up miserable.



Edited by Roocketman (10/20/09 05:07 PM)

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#122712 - 10/20/09 07:16 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: Roocketman]
bigb Offline
member

Registered: 07/05/09
Posts: 124
Loc: Maryland
I've never even heard of vapor barrier clothes, i need to pay more attention.
And I'm being serious!
_________________________
"In the beginers mind there are many possibilities, but in the expert's there are few."
Shunryu Suzuki

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#122717 - 10/20/09 08:56 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: bigb]
Roocketman Offline
member

Registered: 03/10/07
Posts: 203
Originally Posted By bigb
I've never even heard of vapor barrier clothes, i need to pay more attention.
And I'm being serious!


No need to be shocked. There is only one easy to find source for vapor barrier clothing, based on a quick web search. Warmlite by Stephenson at warmlite.com. They use a special fabric that is said to be comfortable, a vapor barrier, and stretchy - key to comfort in next to body or very near body wear.

There may be several sources of vapor barrier sleeping bag liners.

My understanding is that more skill is involved in combining vapor barrier clothing and layers of insulation than just regular layers of insulation. Lack of skill could explain indifferent performance and the resulting low market volume.

It isn't a magic thing that you buy and everything becomes suddenly warm and comfortable and easy.

Ultralightweight backpacking is fairly skill based, and therefore isn't sweeping conventional backpacking gear out into the streets and gutters. It, too, isn't a magic thing that is quick and easy. wink

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#122721 - 10/20/09 10:00 PM Good Information Here Re: (VBL) for sleeping bags [Re: Jim M]
Roocketman Offline
member

Registered: 03/10/07
Posts: 203


http://www.ssrsi.org/Onsite/vapor_barriers.htm

Well now, here is a pretty interesting site discussing the subject. The history of the principle is described... but that may only be "modern" history of VBL. It is easy to think that VBL requires modern materials, and therefore is exclusively modern.

Near the bottom of the page are some words emphasizing that the stuff really shines in VERY cold situations.

Here are some good quotes:

"Before you die of hypothermia from believing those false ads claiming their insulation is warm when wet, I suggest you soak you jacket in a tub of water, shake it out and wear it to experience just how cold it will really be!"

"What is warm when wet? A hot tub! But certainly not any porous insulation used in clothing or sleeping bags."

"To stay warm you must keep those insulations dry. It will not make you any warmer sitting in a freezing wet synthetic fill jacket, knowing it will only take 6 hours [to dry]instead of the 8 hours that a down jacket would take, because you would have a severe case of hypothermia before then!"

"You may have noticed that down is worn by water birds, while dry land birds, like chickens or turkeys, do not wear down. But those water birds always keeps their down dry!"

I hope it is as educational and fun for others to read as it was for me.


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#122738 - 10/21/09 12:22 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: Heber]
Jim M Offline
member

Registered: 11/23/03
Posts: 366
Loc: Kitsap Peninsula, WA
There are two kinds of sweat defined in numerous texts on physiology; sensible and insensible. The sensible is the kind you feel on your skin like when you get too hot. The insensible sweat is the kind that constantly comes off you even though you don't know (sense) it. Sorry if you already know all this, I wasn't sure from your message. And I agree with you. If you stop the evaporation that stops heat loss. (that is just physics: to evaporate 1 g of liquid water, approximately 600 cal are required.It is called latent heat because it reappears when the change of state is reversed.)


Edited by Pliny (10/21/09 12:55 PM)
_________________________
Jim M

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#122740 - 10/21/09 12:49 PM Re: Good Information Here Re: (VBL) for sleeping bags [Re: Roocketman]
Jim M Offline
member

Registered: 11/23/03
Posts: 366
Loc: Kitsap Peninsula, WA
Roocketman,
i read the ssris site page on VB. There is some good, and unusual information there. It was well worth reading. However the article says that insensible sweat stops when it is no longer necessary. That sounds like a quote from Stephenson. i have found that statement nowhere else. There does not seem to be any evidence or support for that statement. To the contrary, there are many studies done in the medical field that seem to contradict that statement. In other words, insensible sweat continues as long as you are alive. If you like I can refer you to some scholarly studies on the subject.
_________________________
Jim M

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#122751 - 10/21/09 05:11 PM Re: Good Information Here Re: (VBL) for sleeping [Re: Jim M]
Cesar Offline
member

Registered: 11/06/07
Posts: 217
Loc: El Paso, TX
I'm taking a shot in the dark but if you are waking up soaked could it be that you were to warm in your bag? So your body is sweating and not just insensible sweat, but sweating to try and cool down, hence the over abundance of moisture.
_________________________
My gear is no where near lightweight

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#122754 - 10/21/09 07:08 PM Re: Good Information Here Re: (VBL) for sleeping bags [Re: Jim M]
Roocketman Offline
member

Registered: 03/10/07
Posts: 203
Stephensen says this:

"Humans have a problem which we are told other animals don’t have: the moisture IN our skin evaporates in dry air, thus losing heat and water. That moisture loss is called “insensible sweat”, which term, like “military intelligence” is an oxymoron (ie, self contradiction). That “insensible sweat” is NOT sweat, and IS sensible: you FEEL it cooling you (but don’t feel it as wetness, thus the “insensible”)."

Insensible sweat is just simple evaporation of water molecules from near the surface of your skin into the air. There are no sweat glands of the insensible type that turn off and turn on for insensible sweat. It is just physical evaporation.



The process is described as evaporation, not as perspiration being exuded as water through the sweat pores.

Sensible sweat is plain old water being exuded from sweat glands and it comes out of your sweat pores as liquid water.

Water sitting in a bowl is similarly evaporating directly into the air, and ordinarily, the bowl will become dry when the water has completely evaporated. There are no perspiration pores in water similar to sweat pores connected to sweat glands in the skin.

However, if the bowl of water is completely enclosed in a waterproof bag, when the vapor pressure of water in the air is equal to the saturation pressure, no more net water will evaporate off of the water surface. [actually water molecules are moving out of the water to the air at the same rate that water molecules enter the water from the air ... so the NET evaporation is zero even if the skin to air evaporation is greater than zero because that is canceled by the air to skin condensation. It is correct to state that the NET evaporation can be zero but the evaporation from the water to the air is not because it only needs to be balanced by air to water condensation for the NET evaporation to be zero.]

However, if the surface of the bag is cold, the water vapor will then condense on the cold bag. This will drop the water vapor pressure and the water will commence to vaporize again .... and you end up with a stream of water vapor running from the bowl of water to the cold bag surface.

[technically, you reach a kinetic equilibrium where the rate of water molecules passing from the skin to the air is the same as the rate of water molecules passing from the air into the skin. NET = 0. For the bowl of water, substitute water bowl for skin in the previous. Just physical evaporation and condensation. Kinetic theory & physical chemistry are one place to see this.]

If the bag surface is warmer than the bowl of water, this bag condensation cannot happen, and there is no water vapor streaming from the cooler bowl to the warmer bag and condensing there because it is too warm to condense there.

If the bag and the water bowl are pretty much the same temperature, whatever water vapor streaming there is is diminished. At a small enough temperature difference, we can say that the evaporation-condensation water vapor transport system effectively stops.

Replace water bowl with water containing flesh and repeat the argument about water vapor transport to the bag wall.

If there isn't a good deal of insulation on the other side of the Vapor Barrier, then the Vapor Barrier bag will be cold and will be an excellent location for condensation of water vapor, and you will be effectively pumping water vapor onto the Vapor Barrier liner where it condenses and makes you miserable and mad and a hater of the idea of Vapor Barrier stuff.


You could get into a situation with a very thin sleeping bag and a very cold night where the (cool) Vapor Barrier liner turns into a cold clammy sweat box. It could be dangerous. But, so is it dangerous with just the very thin sleeping bag on a very cold night.

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#122766 - 10/22/09 02:27 AM Re: Good Information Here Re: (VBL) for sleeping [Re: Roocketman]
OregonMouse Offline
member

Registered: 02/03/06
Posts: 6765
Loc: Gateway to Columbia Gorge
Or, as I found out, with an adequate sleeping bag and an inadequate sleeping pad!
_________________________
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey

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#122799 - 10/22/09 05:53 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: Jim M]
Jim M Offline
member

Registered: 11/23/03
Posts: 366
Loc: Kitsap Peninsula, WA
After reading these great responses I decided to write down my thoughts in my blog. For those who might be interested I will put a link to it below.
http://vaporbarrier.blogspot.com
_________________________
Jim M

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#122827 - 10/23/09 06:48 PM Re: Vapor Barrier Liner for sleeping bags (VBL) [Re: Jim M]
DJ2 Offline
member

Registered: 01/06/02
Posts: 1348
Loc: Seattle, WA
I read your blog. That pretty well sums it up.

On a similar note.....My wife can wear a waterproof raincoat when hiking without getting wet inside. When I wear one there is water running down my sleeves. People are quite different.

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#122838 - 10/23/09 11:40 PM Re: Good Information Here Re: (VBL) for sleeping bags [Re: Roocketman]
Jim M Offline
member

Registered: 11/23/03
Posts: 366
Loc: Kitsap Peninsula, WA
Rocketman: I like the way you think, and I certainly don't have all the answers. Nevertheless, some comments.
Originally Posted By Roocketman
Stephensen says this:

"Humans have a problem which we are told other animals don’t have: the moisture IN our skin evaporates in dry air, thus losing heat and water. That moisture loss is called “insensible sweat”,This isn't really true. Experiments in the medical field on insensible sweat have been done with rats.

If the bag and the water bowl are pretty much the same temperature, whatever water vapor streaming there is is diminished. At a small enough temperature difference, we can say that the evaporation-condensation water vapor transport system effectively stops. Yes, but if the skin is 98.6F I doubt the bag can ever be that warm without an external heat source. What I mean is, you are going to have lower ambient temp outside the skin and hence you would have evaporation.

Replace water bowl with water containing flesh and repeat the argument about water vapor transport to the bag wall. [color:#FFFF99]However, at least one medical journal reported experiments that showed that the insensible perspiration rate was not proportional to the difference between the ambient vapor pressure and the vapor pressure of the liquid in the skin of humans. I don't think the physics of it can explain the empirical data for this.
[/color]
One other issue I ran into in the medical journals was that one study found that it wasn't as easy to tell insensible sweat from sensible sweat. this puts some doubt on our knowledge of sweating in general. For example, perhaps we do produce some so called sensible sweat (from skin glands) all the time that has been mistaken for insensible sweat. But perhaps the most damming research (ie, conflicts with VB theory) was that Sweat (no matter what kind) seems to always be measurable in human skin, no matter the humidity. And it increases with an increase of ambient temp.




Edited by Pliny (10/23/09 11:51 PM)
_________________________
Jim M

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#122847 - 10/24/09 09:03 AM Re: Good Information Here Re: (VBL) for sleeping bags [Re: Jim M]
Roocketman Offline
member

Registered: 03/10/07
Posts: 203
You are an "Artist" trying to make sense of what you read when sometimes authors are unclear on what they are describing, sales and money are involved, and easily available references ma or may not be valid nor relevant.

You began the thread mixing up insensible sweat with sensible sweat. Not a good sign.

I cannot accept your interpretations of "research" you have read as of significance, especially if you don't provide links to the "research".

This is standard scientific stuff.

One takes the word of non-scientists without "fair" documentation as unreliable. It works out better that way, avoiding a lot of wasted effort. Best is to just ignore the subject and not get drawn into it. I am still working on developing that wisdom.

If you look at most of the web definitions of insensible perspiration, they are unphysical.... merely "did you notice sweating" (from the obvious liquid phase present on the surface of the skin). The various web sites appear to be copying from each other or from a common source.

This satisfies lay interests for an explanation, but inhibits clarity of understanding of hypothetical situations - such was what will happen in situations you haven't encountered before. As such, those definitions are relatively useless, from a scientific aspect as well as making predictions.

Scientifically, one expects that as temperature rises, molecular kinetic processes increase their rate. Arrhenius reaction rate theory is fundamental to the understanding of most of the temperature effects that occur. But, not always in a simple "cut and paste" fashion - the underlying phenomena can be different from the easily observed macroscopic event . So expecting insensible sweating to diminish as tenperature increases is contrary to general principles that apply to normal temperature effects in a very wide range of applications.

Just because something seems like it ought to be true isn't reason enough to believe it. (What color are electrons?)

During this "conversation", I have read from Vapor Barrier proponents that one of the reasons for lack of more widespread use of the technique is that it is too hard to explain it to the average customer, and often that sellers aren't well enough trained in it to do so.

I now fully understand this point of view, because I have fully experienced it, and believe that it is unwise to bother to explain it to people. Just, if you have learned how to adopt the VBL situation to your physiology, use it and enjoy it and keep it to yourself.

I have also learned that it was a mistake on my part to reply to you. I will not repeat that mistake.


Edited by Roocketman (10/24/09 09:16 AM)

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#122860 - 10/24/09 04:43 PM Re: Good Information Here Re: (VBL) for sleeping bags [Re: Roocketman]
Echterling Offline
member

Registered: 08/21/09
Posts: 52
Loc: USA
Originally Posted By Roocketman


http://www.ssrsi.org/Onsite/vapor_barriers.htm

Well now, here is a pretty interesting site discussing the subject. The history of the principle is described... but that may only be "modern" history of VBL. It is easy to think that VBL requires modern materials, and therefore is exclusively modern.

Near the bottom of the page are some words emphasizing that the stuff really shines in VERY cold situations.

Here are some good quotes:

"Before you die of hypothermia from believing those false ads claiming their insulation is warm when wet, I suggest you soak you jacket in a tub of water, shake it out and wear it to experience just how cold it will really be!"

"What is warm when wet? A hot tub! But certainly not any porous insulation used in clothing or sleeping bags."

"To stay warm you must keep those insulations dry. It will not make you any warmer sitting in a freezing wet synthetic fill jacket, knowing it will only take 6 hours [to dry]instead of the 8 hours that a down jacket would take, because you would have a severe case of hypothermia before then!"

"You may have noticed that down is worn by water birds, while dry land birds, like chickens or turkeys, do not wear down. But those water birds always keeps their down dry!"

I hope it is as educational and fun for others to read as it was for me.



That quote from that organization read like ad copy. So I Googled it and it came up at Warmlite.com too.

I have to wonder about anyone that suggests it is impossible to be warm while wet. I've spent significant amounts of time in cold wet places, and I've been soaked thoroughly, but comfortable and safe. Synthetic insulation does indeed keep me warm while wet.

This leads me to take a critical eye towards anything they've written.
_________________________
--------------------------
My blog

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#122894 - 10/25/09 10:55 AM Re: Good Information Here Re: (VBL) for sleeping bags [Re: Roocketman]
ringtail Offline
member

Registered: 08/22/02
Posts: 2296
Loc: Colorado Rockies
Hey Roocketman,

There is a water proof and breathable membrane that we all have used -- skin.

I first used vapor barier technology as a Military Policeman. A dry cleaning bag over pajamas (yeah cotton) then the regular wool uniform. Worked great. A sandwich of cotton T-shirt, dry cleaning bag and cotton hoodie was great for a jog.

I carry and use vapor barrier technology hiking 3 seasons. A sandwich of regular socks, produce bags and fleece socks keeps my feet warm.

There is no commercial reason to promote vapor barrier use. One of the best is an emergency rain suit sold at Wal*Mart for about $6. The competition is a $250 high tech parka.

Vapor barrier clothes work great when you level of physical activity is constant. It requires frequent layering for most activities.
_________________________
"In theory, theory and practice are the same. In practice, they are not."
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09/24/21 12:29 PM
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