These experiences inspired me to look into vapor barrier suits when I got serious about lightweight winter backpacking.  I figured that a 30 denier, zero porosity nylon "sweat suit" could be lightweight, add ten to fifteen degrees of insulating value to my sleeping bag, prevent me from dehydrating overnight and keep my bag dry.  I also thought that it could be worn when I had to get up at night, could be used as a base layer in camp and might even make a dandy emergency garment.

So, I began experimenting, and over the next several years I found that all the imagined benefits of a vapor barrier suit were real.  I also discovered two other things.

Unlike vapor barrier sleeping bag liners, a two-piece vapor barrier suit can be sealed effectively at the wrists, ankles, waist and neck.  A suit also encloses a much smaller volume of air than a liner, and, immediately upon putting it on, the suit's two "micro climates" begin to warm up and humidify.  Once a certain level of humidity is reached, the body no longer needs to produce moisture in order to keep the skin supple, so it shuts down the insensible production of sweat.  Because sealing keeps the warm, moist air from being replaced by cold, dry air, this "no sweat" condition endures until the suit is removed.  I find that I'm just barely damp when I take my suit off in the morning.

In addition, I found that a vapor barrier suit is a better insulator if it's made of reflective material.  In effect, a combined vapor barrier/radiant barrier suit can serve as a wearable Space Blanket^TM.  However, in order to get the full benefit of the radiant return there needs to be a thin, non-absorbent layer of material between the skin and the suit.  I now wear Patagonia^TM silkweight stretch Capilene^TM underwear under the suit, and I find the addition of this layer makes the suit much warmer, more comfortable and easier to get on and off.  When I get into camp, I take everything off but the underwear, don the suit, and then put my "activewear" back on.  If the "activewear" has become damp during the day, it will dry quickly when worn over the suit.  Further, the underwear stays dry enough that I don't have to take it off until I get home or can't stand myself.  

The vapor barrier smock and pants I use now incorporate both vapor barrier and radiant barrier technology.  They also use external closures at the wrists, ankles and neck, and shock cord closures at the waist.  This closure system allows near-perfect sealing.  It is also comfortable, adjustable, washable, eliminates elastic rot due to sweat absorption, allows the garments to be vented and makes getting into and out of them easy.

Both the smock and pants are made of a highly reflective, silicon coated, silver rip stop nylon.  Smock and pants weigh 4 ounces, each. The full suit adds ten to twenty degrees of warmth to whatever I wear over it, prevents me from dehydrating when it's worn overnight, and keeps my sleeping bag clean and dry.  I use the suit all winter, but also take it on those early spring or late fall trips "just in case."  While it's designed for cold weather, I've worn it comfortably in fifty degree temperatures.  Because I heat up so much when I'm active I've never had to wear the suit during the day, but it can be vented if used as "activewear."  In a pinch the suit can serve as short-term rainwear.

My vapor barrier mitts are made of the same material as the smock and pants, and are designed to function in several ways.  First, I wear them alone in the spring or fall as windbreakers or handwarmers.  Second, I've sealed their seams so they can be used as rain mitts, and their long gauntlets allow them to work especially well with a poncho.  Third, when the gauntlets are tucked into the sleeves of my vapor barrier smock they become effective vapor/radiant barriers.  Finally, they are cut large enough so that I can wear them as waterproof winter overmitts, using Sealskins gloves as a base layer and fleece mitts as an insulation layer.

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