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Posted by calamity on December 9, 2007 at 2:00:37 am EST
In reply to Re: Sleeping bag liner posted by Bill S on December 8, 2007 at 1:31:18 am EST

I stopped experimenting with vapor barrier liners mainly because when it's cold, the idea of stripping down to long underwear to get inside a sleeping bag is unappealing. Also, I almost never camp in winter for more than one consecutive night, which significantly reduces their potential advantage.

Or maybe I quit because of the (rather slight) discomfort from claminess. I never made a real decision about VBLs -- just abandoned them. Thus, I'd be very interested in any actual experience that others have with the things.

As far as my tentative impressions went, they seemed to work okay. One often reads that they must be used only in temperatures well below freezing. But two of the five nights I tried them (both duct-taped garbage bags and sewn jobs) were in lightweight bags with temps around 40-50 degrees, and I noticed little difference in claminess or discomfort, compared with the other nights, around zero. Indeed, it well be that my fears of dampening pile jacket and other layers are unfounded.

Apart from the warmth resulting from loft retention, one hears that they add to a sleeping bag's warmth by halting evaporative cooling. An additional warmth of 10 to 15 degrees from this factor sounds like a credible maximum to me, with most of it kicking in in colder weather.

So if they're so great, how come I don't use them? Dunno, exactly.

Individuals vary a great deal in the amount that they sweat though I would think the range of variablity while sleeping would be (much?) smaller than while exercising. Perhaps this variablity influences the effectiveness of vapor barrier liners. In any case, I sweat less than some people. Also, most likely, atmospheric conditions are a relevant factor.

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