vapor barrier

[Biloxi]

does anyone have any expieriance with a vapor barrier liner? how would it perform with a down bag? and how much more warmth would it give?

[hikerjohnd]

No first hand experience, but doesn't the manufacturer give the added warmth claim? I assume it is similar to a liner - 5-15* of added warmth depending on their claims. As to adding to a down bag, it should add the specified warmth with no problems.

[fiddlehead]

Yeah, i've tried them. Not very comfortable as you are getting in there naked, and closing the neck up tight, and then you sweat and it gets very clammy.
But they do keep you warmer than not. Just not a pleasant night either way.
they are lightweight but i only used it in an emergency one night when the temps dropped down to single digits and i had my 20 deg. bag. (i'm a cold sleeper)
Back in 89, many people were carrying them although not too many had pleasant things to say about them.

[The Will]

does anyone have any expieriance with a vapor barrier liner? how would it perform with a down bag? and how much more warmth would it give?

Used properly, vapor barrier liners (VBL) can significantly extend the range of your bag. The rationale is that your body is continuously sweating (the word "sweating" being used very loosely here) even in cold, dry conditions to maintain a certain degree of humidity on the skin for conditioning purposes. This amount moisture output, especially in the context of sleeping in a sleeping bag on a cold night, is insensible to the touch, but still contributes to some evaporative heat loss. VBLs retain that insensible moisture and maintain an appropriately humid environment around the body so that once the physiologically ideal humidty is reached, the body discontinues the moisture output. Because the VBL provides a semi-sealed package around the body, evaporative heat loss is nearly eleminated.

As a previous poster noted, this can be a clammy and unpleasant experience. As a remedy, I sleep fully clothed inside a VBL: full long-johns, hat and even gloves. I want to avoid my skin touching that VBL. You'll only want to use the VBL at the very lowest extremes of your bags temperature rating. For example, if your bag is rated to 10F, than it would be appropriate to use the VBL in temperatures hovering just above 10F down to zero or less. (I have used my 10F bag plus a VBL and hot water bottles and slept down to -20F. Certainly I could have been warmer, but I was warm enough to sleep soundly and it was due in large part to the VBL).

I hope this is helpful.

[Rambler]

Vapor barrier liner is designed for the down bags to not only add warmth, but to kepp the moisture given off by your body from getting into the down. Artic explorers found that when their down bags became wet from body moisture the bags froze solid during the day. They had a hard time getting into them at night, having to warm them up, thaw them out inch by inch. Do not think you'll have that problem unlesds you are out for a long winter's expedition. Warmlite bags actually have a vapor barrier fabric lining their bags. A nice compromise to the full vapor barrier you mention is to use vapor barrier clothing like a rain gear pant and a vapor barrier shirt of some kind. These can then be worn during a cold day or as windbreakers, so they provide you with a dual use, one for swleep wera and another use during the day. The clamy feeling you may get from vapor barrier next to your skin quickly evaporates when you remove the garmet or get out of the liner.
End result...they work so so!

[Footslogger]

For those who have experience with Vapor Barriers ...what would you think about something like this to add some warmth and waterproofing to a sleeping bag ??

http://www.backcountrygear.com/catalog/bivydetail.cfm?PRODUCTS__ProductID=EQ3000

Been considering one of these for quite a while now for the above reasons.

Thanks in advance ...

'Slogger

[LostInSpace]

I have never used a VBL, but I would think that one could sleep in their rain gear inside their bag and get somewhat similar results, but obviously not as effective as a VBL.

[Just Jeff]

I've used my raingear like a VBL. It helps a little.

One night, I put on my fleece jacket under my rain jacket and it was damp when I woke up. The next night I put my fleece jacket on the outside and it was much drier. I don't remember it making much difference while I was sleeping, but that sure made getting out of my hammock more pleasant. It was a wp/b jacket, btw.

Two things make rain gear less efficient - it's usually breathable to some extent (goretex and the like) so it presents only an "obstacle" instead of a "barrier" to vapors. Also, VBLs rely on a lack of ventilation so no moisture can escape. Rain pants and jackets are usually not designed to completely restrict ventilation, so some moisture will be released through the zippers, neck opening, waist, etc. Releasing that moisture means your body will create more, which means you've lost some heat from evaporative cooling.

But I do sleep warmer with my rain gear on so I agree with your post.

[NECKBONE]

I carry a vapor barrier bag for emergencies and also my sleeping bag & clothes bag go into it at the bottom of the pack. Therefore, it's the old thing of duel usage. neckbone

[mweinstone]

a vbl is only for sub arctic cold. its function is to keep insulation dry. its side effect is to otherwise extend the range of a bag. but they arent used to do that . only in conditions where dispelling moisture into insulation is deadly. thats it. get a regular liner or use a bag warm or versitile enough.

[Just Jeff]

Matthewski, that was a completely coherent and rational post with no mention of your shaven idol. You ok? :p