Making my own Vapor Barrier Liner for a mummy sleeping bag
I'm trekking up the Kilimanjaro and planned on using my sleeping bag which is rated for -10 / +10 with an extreme at -17 degree Celsius. I read that temperatures may plunge down to -25° at the very top, although I don't know how cold nights at the camps are to be.
I was planning on making my own Vapor Barrier Liner in case I get cold, despite the bag and my cotton liner.
My plan is to use a heavy-duty garbage bag (to prevent moisture from leaving), add infrared radiation reflection with a thermal blanket inside of that, and to make things cozy, slip in my cotton liner.
Is this a decent homemade vapor barrier liner? If not, how can it be improved? Also, how damp may my cotton liner be in the morning with such a system?
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I like this article on vapor barriers. Your trash bag will act as a very good vapor barrier on the parts of your body that it covers. You are going to need a really large garbage bag, or a hole cut in the bottom, in order to cover your torso. Garbage bags, even the heavy duty ones, are not that durable, so you may need to bring one for every night.
It sounds like your plan is to put a cotton liner inside your vapor barrier. I This is pretty close to the worst thing you can do. The vapor barrier, if working correctly, will trap about 0.5 liters of perspiration every night. In the ideal world you would achieve 100% relative humidity within the vapor barrier and everywhere the cotton liner is, which I think will reduce a lot of the chilling effect of the cotton, but more likely there are going to be gaps in your vapor barrier and the cotton is going to be a bad idea. Soaking a cotton liner in 0.5 liters of water is going to lead to a chilly night. You would be much better off putting the cotton liner on the outside of the vapor barrier. In that case, if the vapor barrier is working, the cotton liner will stay dry, but of course you will be sleeping in the clammy hell of a vapor barrier liner (but you will be warm).
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I would consider a polyester or wool liner before one made of cotton. Cotton is quite comfortable dry but not so much wet. Andrew Skurka has a lot of experience with vapor barrier and wrote a good article about it.
How damp will it be is dependant on how well your thermoregulation is. I would definitely recommend trying your system before hitting the mountain.
For me, vapor barriers are interesting on long, multi-months, trips. Just make sure that if you get cold on top of the mountain you don't end up cold and wet with your vapor barrier!
This post was sourced from https://outdoors.stackexchange.com/a/5093. It is licensed under CC BY-SA 3.0.
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