Sleeping outside in the winter time in New England can be a challenge. With the right combination of gear and a little common sense, getting a good night’s sleep isn’t such an ordeal. We’ve discussed the benefits of insulation underneath (foam – air – foam) and most of us already know about the power of goose down. With the addition of an outer cover like a bivy bag, you add weather resistance and lower temperature rating for your system. The missing component, the piece that will lower your sleep system’s temperature rating even further AND extend the life of your sleeping bag’s effectiveness is moisture control in the form of a Vapor Barrier Liner.
Goose down is the best all around insulation for sleeping bags. Down is light, it compacts to a tiny size for easy packing and it has an amazing longevity if cared for correctly. Get goose down wet, however, and it is pretty much useless. That is because goose down can trap lots of air within the “loft” of the feathers. It’s that dead air space between those tiniest of feathers that gives goose down its legendary insulating properties. Those feathers get wet, however, and they lose that loft and all that trapped insulating air. Even a tiny bit of moisture will rob the feathers of their insulating loft, reducing that expensive goose down sleeping bag to a lump of cold, useless weight in your backpack.
If you’re planning on spending more than an overnight sleeping outside, you’re gonna want to keep your goose down bag dry to mantain its insulating qualities. Of course you’ve wrapped up your precious down “Boy Scout” style to keep the wet off when your hiking in, right? But what about the water from YOU. A sleeping person can generate more than a 1/4 cup of sweat in the form of goose down soaking water vapor. Yes, its possible to dry your bag winter hiking, the air can be exceptionally dry and hanging your bag directly in the sun can do the trick in a hour or so. But you don’t have to rely on the sun, slipping into a Vapor Barrier Liner will keep that moisture from reaching your goose down.
A Vapor Barrier Liner sounds icky, like an oven roasting bag used to cook meats in their own juices. The VBL does create a period of “moistness” shortly after you climb inside. This is only temporary, however. I find when inside this sleep system, my skin sweats out to a near salamander state, over moist and, yes, mildly uncomfortable. Wait it out and the amazing properties of human epidermis kick in. Human skin, epidermis, is the body’s largest organ with amazing features. Imbedded sweat glands, multiple cell layers, hair follicles, sensory nerves; this complex system has evolved as a first line of defense against the elements, including cold. For your skin to work properly, it needs to adjust to any change in its environment. That initial moistness will soon give way to a more comfortable “skin conditioning” micro environment inside the impervious bag. Once the skin has “over compensated” the moisture level as a response to the sudden warmth, the epidermis “shuts down” the sweat factory, drying out a bit. Eventually, human skin settles at the right level of moisture that is so important for maintaining its insulating properties.
Wrapping yourself up in multiple layers of nylon can be a bit claustrophobic; the price you pay to insure a warm night’s sleep. Since you’ve removed most of your “layers”, leaving you clad only in a wrapper of polypro (or some synthetic first layer), there is more freedom of movement than you might expect. You’ll slip in and out of your sleeping system like, ah… ummm, well, you get the idea.