We can add a bit more to the VBL description. In a typical night while at sleep an adult male looses water via insensible perspiration and respiration. To transform water into vapor requires heat energy, between 2,000 and 4,000 BTU per night depending (body size, humidity, metabolism etc.). This is a source of dehydration but the heatr loss is the most crucial factor. It takes 55 btu to make a cup of coffee on an average cool camping morning. (Dave Kruger can add the details). 2,000-4,000 BTU is a lot of heat. So the VBL does two things: first it saves most of that heat -- once the ambient humidity next to the skin reaches 95% or so perspiration stops, so no more water need be turned into vapor, so no more heat is lost. If the VBL is close to the skin only a small space need be kept humidified. Second, perspiration without a VBL passes though insulating layers until it reaches colder air, like near the inner surface of your sleeping bag, then recondenses into liquid or freezes into solid form. Now you have an ice filled sleeping bag. The same thing happens in mountaineering and ski touring boots which is why many of us used to wear plastic bread bags over our liner socks and under our thick Ragg socks on winter climbs and ski tours. The practical effects of VBL are, in our experience, not a 5 or 10% increase as was suggested by another poster but a 10 or 12 *degree* F improvement in the comfort rating of our bags (consistent over 20 years in varied conditions) not to mention keeping the insulation dry and therefore as lofty on the second and third days out as on the first. Even kayakers and canoefolk sometimes uses VBLs. I once led a group of novice paddles to the Broken Group in March. A rare calm day made our crossing to Hand island uneventful but the temp dropped to 10 F that night and many equipped with summer habits and gear were cold. I gathered the frigid folk together around 10:30 and gave a little VBL lecture. Basically I told everyone to strip to there long johns or a thin inner layer, then put on their rain coats and pants (tucked into socks). We used water proof stuff sacks and the like to cover feet. Then everyone got "dressed" again in pile and other insulating layers *over* these impromptu VBLs. All but one unbeliever slept fine from then on. I had my trusty Camp 7 commercial VBL and was happy as can be. Happy paddling and warm ski touring. Rich Richard Culpeper wrote: > > A vapor barrier is a diaper for your sleeping bag. It is a thin waterproof > bag which fits between you and the inside of your sleeping bag. It > prevents your perspiration from getting into the sleeping bag. > > Richard Culpeper > www.geocities.com/~culpeper > > ---------- > > From: Bob Denton <BDenton_at_aquagulf.com> > > To: Paddlewise (E-mail) <PaddleWise_at_lists.intelenet.net> > > Subject: RE: [Paddlewise] Re: Sleeping bag liners-VB > > Date: Tuesday, October 20, 1998 4:22 PM > > > > What is a Vapor Barrier? > > > > > > > *************************************************************************** > > PaddleWise Paddling Mailing List > > Submissions: paddlewise_at_lists.intelenet.net > > Subscriptions: paddlewise-request_at_lists.intelenet.net > > Website: http://www.gasp-seakayak.net/paddlewise/ > > > *************************************************************************** > > *************************************************************************** > PaddleWise Paddling Mailing List > Submissions: paddlewise_at_lists.intelenet.net > Subscriptions: paddlewise-request_at_lists.intelenet.net > Website: http://www.gasp-seakayak.net/paddlewise/ > *************************************************************************** -- Richard G. Mitchell, Jr. Department of Sociology Oregon State University Corvallis, OR 97331 U.S.A. (541) 752-1323 phone/fax mitchelr_at_ucs.orst.edu *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************Received on Wed Oct 21 1998 - 21:54:04 PDT
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