Originally Posted By OregonMouse
VBL = Vapor Barrier Liner

I use one (actually my non-breathable rain gear) inside my sleeping bag when it's below freezing. It keeps moisture from my body from condensing inside the outer shell of my sleeping bag and wetting out the down. I wear the suit over my base layer. If I need more clothing to help the sleeping bag keep me warm, it goes over the VBL so it stays dry. Note that my system will NOT work with waterproof/breathable (WPB) rain gear! My rain jacket and pants are silnylon.

Individuals differ as to what temp a VBL is comfortable. For me, it's right around 32*F/0*C for sleeping. I haven't tried a VBL for active moving--it doesn't get that cold around here. In other words, it takes some experimentation.

Good article here.
Great article! Thanks OM, I was reading where some use it all year, with proper ventilation durring warmer months. I was looking at some bag liners as I've found I sometimes get quite a bit of sweat accumulate on my pad when camping for one to two weeks in single digit temps.
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