Vapor Barrier Liner/Pack Liner

I'll have some pictures and text descriptions up soon of this concept. In a nutshell, though, the VBL/Pack-liner is a large, moisture-impervious bag that will usually function as your pack liner, but that can also be used as a VBL inside your sleeping bag in very cold conditions when the sleeping bag itself just isn't keeping you warm.

As a pack liner, it serves as a lightweight, long-lasting, interior barrier to prevent moisture reaching the contents of your pack. While similar in function to a large garbage bag or a leaf bag, a pack liner that is constructed of Sil-Nylon will last much longer, provide better long-term water protection, and weigh very little more than a plastic bag. The fact that it can also function as another piece if gear is what really sets it apart.

This other function is when you need it as a Vapor Barrier Liner for use inside your sleeping bag. A VBL inside your sleeping bag serves to stop evaporative heat loss - that is, heat lost due to moisture escaping from your skin while you lay in the sleeping bag. Putting it simply, this type of moisture loss may not be detectable to you, but it is always happening, a slow, light type of sweating. Sweating cools your body down. Because it will not let your moisture escape, the VBL traps a local region of complete humidity next to your skin, and soon enough your skin will stop losing moisture, and therefore heat.

For example, my first experiment with VBL a few years ago: I used a cheap 20 degree synthetic bag (so it probably didn't even really work down to 20 degrees) and one of my tents in a mid-January snowstorm. Temperatures that night I later learned were officially recorded at 14 degrees, with a Wind Chill Factor of -26 degrees. Yep, *minus* 26. Although I was in a tent, I had the vestibule fully raised, so that airflow would be impeded as little as possible - I wanted to be cold, as cold as possible, while I did this test. Stripping off my clothing, I jumped into the VBL/sleeping bag, and lay there for a few moments while my body heat warmed up the VBL and bag. I'd heard that VBL's could be uncomfortably clammy, but the only moist sensation I noted was a little around the feet. I fell asleep around midnight, and slept until 9:30 the next morning, comfortably and without awakening. I was *very* impressed. The worst part of the whole thing was having to get out of the warm sleeping bag/VBL :)

The VBL has become a staple item in my both my pack and my kayak since then. I used it for 4 nights in a row once with wonderful efficiency during a week-long, early spring paddling trip on the coast of Georgia. I got caught out there with a 40 degree bag during a succession of 20-30 degree nights, and the VBL is what allowed me to finish the trip successfully. It really saved my bacon :) About the only time I don't carry it is in very warm weather.

These figures are approximate: Weight 3-4 ozs, Size 30"x72", Price $25