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The Vapor Barrier

by Luigi Seli

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The Vapor Barrier by Luigi Seli
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It was mid October when we left for our last hike of the year. The temperature high on that first day was 65F, so we knew we were in for a chilly night. As we started settling into camp that first evening, the sun dropped behind the mountain range and it felt like the temperature instantly dropped 10 degrees - funny how that happens up high in the mountains (we were at ~10,500 feet). My buddy started scurrying about pulling out all his cold weather gear; goose down parka, polartec vest, heavy wool shirt, thermax long sleeved T-shirt, thermax long-johns, polartec sweat pants, wool cap, and wool gloves. There he stood, all decked out to do battle with the cold, looking as wide as he was tall. Poor fellow could barely move about to do any of his camp chores, and surely without the slightest bit of grace or dignity. I, on the other hand, put on my vapor barrier (VB), a long sleeved thermax T-shirt, a heavy wool shirt, thermax long-johns, polartec sweat pants, a wool caps, and fingerless wool gloves. My buddy looks at me and says "putting plastic against my skin is a sure way for me to be miserable." This is the unfortunate presumption made by most individuals on the use of a VB.

"What the heck is a vapor barrier or VB" you ask. It's a barrier between your skin and the elements, and plastic works best. I use a tall kitchen trash bag and cut holes out for my head and arms. The two basic principles behind the use of a VB are as follows:

1. The colder it is, the better a VB works (I personally would not even consider using my VB unless I were exposed to temperatures below 50F for any considerable length of time). The warmer it gets, the more a VB loses its comfort value.

2. The closer to your skin (preferably on it, but T-shirt, VB, T-shirt will give 90% of the results) the more effectively a VB will perform. A VB worn away from the skin can cause gallons of water vapor. Example - a waterproof parka/anorak is essentially a VB worn away from the skin, and I am sure you are aware of how sweaty you can get in rain gear; this event alone is what prompts most individuals to be skeptical about VBs.
Body heat makes the difference! Since the VB is warmed by the body, the body's comfort layer (more on this to follow) is easily maintained directly on the skin with minimal vapor output. If the VB is not kept warm, as with rain gear, the temperature differential will invite you to sweat.

HERE ARE SOME INSIGHTS ON THE MYSTERIES OF A VB - based on research (Robert Wood) and practical experience:

The skin, as a highly sensitive organ, likes the air temperature on it to be about 75F, ranging from 72F in the hands and feet area to approximately 78F in the head and upper torso area. So what the body (your skin) wants is a quarter inch layer of moist air protecting it at all times. Moist does not mean wet - moist, comfortable skin feels dry to us, truly dry skin will quickly chap, crack, and soon bleed. Disrupt the protective (comfort) layer and the body goes wild trying to restore it.

If you heat up the comfort layer, the sweat glands open up and start pumping out water vapor to cool the body back to that optimal comfort zone. If you cool down the comfort layer, the sweat glands shut down and the body starts to shiver, again, trying to regain that optimal comfort zone. A VB works because it utilizes, rather than ignore, the body's continual water vapor and heat production activity.

Here is a practical example of disrupting the skins comfort layer - on a 68F day you can comfortably walk to the store in a long sleeved shirt, but try jumping into a 68F swimming pool - it'll feel like ice water. On the 68F day your body can easily maintain a 75F comfort layer, but in the water it cannot; the sudden 7F drop on the bare skin is a shock.

As outrageous as a VB sounds, informed consideration of our bodies behavior shows it to be perfectly logical. World War II ski troops afflicted with trench foot and frostbite from continuously wet, cold feet had their dilemma miraculously solved by the use of VB socks, which also solved the frozen foot problem during the Korean war. A properly used VB will increase body warmth by 20F.

The concept of a VB contradicts all our good sense about staying dry and comfortable, and the system takes some tinkering and getting use to in the field. As the temperature gets milder, the system's efficiency makes overheating rather easy. The basic field use concept is that a VB requires ventilation, if not removal, in weather that's warming up, or when physical exertion raises the skin temperature near the sweat level. So, don't JOG to the top of Whitney with a VB on!?!

The preceding is a simple brush on the details of the effectiveness, use, and benefits of a VB, and is not intended to challenge anyone's opinion. I merely wanted to present the perspective of a devout user and believer of VBs. One of my staple survival/cold weather kits is a tall kitchen trash bag for my torso (essentially a plastic vest) and two produce bags (the ones from the market) - one for each foot, and they have kept me comfortably warm through some rather adverse conditions (Mt. Whitney in late April).

If you are skeptical, consider conducting this simple test on your next outing in order to demonstrate the virtues of a VB. On a COLD morning, or evening for that matter, put the following on ONE foot - a produce bag (directly on the skin), a sock, and your boot. On the OTHER foot put on a sock and your boot (if you wear camp socks and shoes, use them instead, the effects will be more dramatic). Then go about your morning/evening camp routine and you will be amazed at the comfort difference in each foot.

So now you ask, "why aren't outdoor magazines raving about VB's?" Economics, my friend! Do you think that outdoor clothing manufacturers would continue to spend tens of thousands of advertising dollars in a magazine that runs articles touting the virtues of a 5 cent alternative to the $200.00 - $300.00 whiz-bang parkas being advertised!

Well, I have rambled on long enough. As you have gathered, I am a true believer in the use of VBs, but I also recognize that one man's treasure can be another man's rubbish. Happy Trails!

About the Author

Lu Seli (lseli@gnp.com) lives in the Los Angeles area with my wonderful wife and our three terrific kids. I am a Quality System consultant for the manufacturing in


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