Vapour Barrier Liners
One of the well-known dangers which comes with time spent in extreme cold can be moisture coming off the body and getting trapped in the insulation of your clothing or sleeping bag. And it's not just when you're sweating. Insensible perspiration is always coming off the skin and in time amounts to a considerable volume of water.
The resulting damp insulation is much less efficient and makes you feel cold when the moisture starts to evaporate. But worse than this, the freeze-point is often in the middle of the insulation and the build-up of ice progressively reduces warmth and adds weight.
These days polar explorers and high altitude mountaineers often use VBL's (Vapour Barrier Liners) to minimise this problem. A non-breathable layer inside the main insulation traps the escaping moisture, so that the insulation stays dry and ice free.
The downside to VBL's is that they can feel clammy. But if used with wicking thermal underwear inside (or a pair of socks in the case of VBL socks), the discomfort is slight and more than outweighed by the increase in overall warmth and efficiency.
Apart from the actual VBL items we offer (our VBL bag), most PHD insulated products can be fitted with VBL inners if required. This added extra is worth considering if you are going to spend several days or weeks in extreme cold away from a base where your gear can be adequately dried out.
Please note: Our VBL socks have been withdrawn until we can find the right lightweight fabric for the job.