Underwear Or Outerwear?
Making Sense of All the Fibers.

Outfitting yourself with long underwear used to be such a simple thing. However, with so many confounded layer thicknesses and fabric weaves and types added to the mix the lines defining where underwear ends and outerwear begins are no longer clear. This guide to selling underwear should help you cut through the layers and get right down to the essentials-meeting your expectations of staying warm and dry.

Weighing In
Thick or thin, special weaves or not, the primary intent of a base layer / underwear is to manage moisture (wick or transport perspiration away from your skin) while adding a degree of insulation. How much insulation you will want depends on how cold the environment will be coupled with your anticipated level of activity.

In general, underwear is offered in three weights: lightweight for high aerobic activity and moderately cool temperatures; midweight for optimum versatility, warmth and wicking when backpacking, fly fishing, skiing, snowshoeing or hunting on the move in cold temperatures; or expedition weight for high warmth when activity or movement is limited and the temperatures are quite frigid.

Dispelling Myths

Regarding Cotton
Cotton does not insulate; never has, never will. If you are still clinging to an old cotton union suit as underwear, do yourself a favor and only wear it to bed, never outdoors. The only time that cotton should become a part of your base layer is if you wish to keep cool, not warm.

Regarding Polypropylene
Polypropylene (the original synthetic fiber for underwear) does not wick or absorb moisture. Polypro is, you see, water hating or hydrophobic, and cannot wick or transport moisture without help. With no outer or second clothing layer to absorb moisture, your perspiration can puddle right next to the skin. Yes, it's true that your body heat will "force" water vapor through polypro, but this is not wicking, no matter who argues the point--it's evaporation and even under the best of circumstances, evaporation can only dispell so much moisture build-up.

As for solid performance at a very economical price, polypropylene is a superb value and will keep you warm and dry without breaking the bank. Just don't forget to place a wool or fleece sweater or shirt on top of your undies to serve as a wick to pull moisture away from your skin. New microbials (bacteria hating / smell eliminating) weaves of polypro are better than ever so no one can point a finger at you claiming you stink--at least not because of your underwear.

A Synthetic Fit
When fitting synthetic underwear, opt for snug and close-fitting, but not constricting. If you fit your tops and bottoms too loosely, they won't wick or transport moisture efficiently away from your skin and you'll wonder where you lost the performance you heard you'd be getting.

There are exceptions to every rule, so be sure that you understand the manufacturer's individual fit instructions. One such exception would be the nylon-based Transport EC2 underwear from Terramar. Molecularly enhanced function improves wicking and moisture evaporation and allows for a moisture transfer process that doesn't require the fabric to actually touch the skin to work. What this means is that the fit can be loose and comfy.

From Basics to Blends
Bicomponent knits such as polyester / wool or polypropylene / wool blends work to provide wicking and insulative properties in one layer-the side facing your skin is water-hating while the side away from your skin is water-loving and pulls moisture through. The one drawback to this approach is that because of the wool, the underwear takes longer to dry.

Magic Through Chemistry
Chemically treated polyesters such as Capilene, Thermal Dynamics and MTS are often blended with Lycra for stretch and better fit performance, and nylon for durability. By itself, polyester doesn't manage moisture well at all, but when treated with a water-loving chemical process, moisture is encouraged to migrate through the fabric to the outer surface where it can evaporate. The trouble is, the chemical washes out over the months and after a year or two of hard use, your underwear can end up feeling flat and clammy.

Variations On A Theme
A variation on chemical altering is MontBell's DriOn with O.F.T. (available through Lands End). DriOn is made with a molecularly altered polyester yarn so the treatment won't wash out and relies on an electrostatic field to "bounce moisture" along the fabric thereby increasing evaporation. O.F.T. stands for Odor Fighting Thread and while I wouldn't toss the antiperspirant just yet, I have found that it does seem to minimize, ever so slightly, the retention of odor that many synthetic underwear are infamous for.

Weaving In the Function
Another construction approach is to alter polyester structurally, creating weaves and shapes that actually encourage the polyester to absorb water and "pull" the moisture away from your skin. Underwear constructed of Thermax, CoolMax and Thermastat are all common brand names, dry very quickly, insulate very well and feel super soft, however they too have their downsides. For one, the process isn't cheap and it is possible, if your perspiration level is very high, for these fabrics to absorb so much water that they get saturated and stop functioning, leaving you feeling like a damp sponge.

The Best of Both Worlds
Malden Mills has brought together the best of both chemical and structurally altered polyester and created their own fabrications dubbed BiPolar 100 (midweight) and BiPolar 200 (expedition weight) with the intent of wicking better and offer more warmth for the weight than comparable underwear. BiPolar also offers a soft, warm and cushy feel against the skin and many of you will be inclined to wear it both as underwear and a comfy outer layer.

Going Natural
New weaves and precision cutting tools have virtually eliminated the age-old, and well deserved reputation wool had earned as being heavy and scratchy. Today's woolen underwear has a kinder and gentler feel while still performing as an excellent insulator even when wet. Since wool is also made of protein and keratin (sulfur-containing fibrous proteins), sweat is neutralized so bacteria growth is inhibited.

Meshing Performance
Some companies, such as Wiggy's, have opted for a mesh construction for the base layer. The intent is to create a base layer that enhances moisture transport to outer layers, thereby keeping the body's skin dryer and, consequently, warmer. While it does work quite well, the pattern it leaves on your skin after an hour or two of wearing a pack is, at best, an interesting conversation piece.

Don't Compromise Performance
While underwear can very often be used as outerwear and worn as a second or third layer, the only way it will work as a moisture management tool is as a first layer. That said, you need to remember that wearing cotton briefs under your undies will add an unpleasant chill to the thermal equation.

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