Choosing Base Layer

Depending on where you grew up, you might talk about staying warm by wearing 'long handles,' 'thermals,' 'long johns,' maybe even your 'union suit.' They all mean the best way to stay warm-a good insulating layer under your clothing, next to your skin.

By trapping heat as it comes off you, base layer can be much less bulky and more efficient than layers added over your clothing. Additionally, as you warm up and perhaps sweat a bit, good baselayer will keep you more comfortable by wicking that moisture away and out to other layers where it evaporates.

Materials

For generations, cotton was the option for long underwear. The bulk and air-trapping waffle knit certainly are cozy, but can seriously impede range of motion, and when wet, cotton loses what little inherent insulation value it started with. In the current market, there are many choices on either the natural or synthetic side.

Merino wool is not new, but the manufacturing techniques currently used mean it is more comfortable and performs better in a wide range of conditions. Natural fibers all allow air and moisture to penetrate, so air moves through very easily. Because wool is an inherently insulating fiber, it will keep you warm even when wet, and has excellent warmth-to-weight ratio, meaning that less bulk returns more insulation than comparable synthetics. Wool also has natural 'return' or stretch, so 100 percent of the fabric is insulating and breathing.

Silk is still an option from a few companies, but most silk fabrics are woven and have little stretch or durability, as well as offering fewer weights and construction options, and the inherent warmth is about the same as similar weight synthetics.

Polyester fibers like Capilene are spun in so many ways now that the same basic material shows up in silkweight wicking pieces as well as beefy expedition-weight tights and tops that perform at the top of the world. With hollow cores and a hydrophobic nature that sheds water, the synthetics win the quick-dry race every time. Knit fabrics with 'mechanical stretch' can provide excellent skin contact without additional elastic fibers that can reduce wicking and insulating properties.

In the last few years major league athletes have adopted compression garments under their uniforms, especially in the winter months. While the high elastic content works well for the duration of a practice or game, most close-fitting next-to-skin layers can become very uncomfortable after an eight or ten hour day on the slopes. When used in the backcountry where laundry and bathing are infrequent, high-elastic base layer can lead to skin problems as the daily buildup of oils and dirt is held against the skin. Additionally, elastic fibers cannot insulate or wick moisture, so when checking content tags, imagine that the percentage listed of Lycra or Spandex is that much less comfort for you at the end of the day.

Deciding

So which is better, merino or polyester? It really depends on how warm the weather might be and how often you'll be doing laundry.

Wool is absorbent, so it will dry slowly once you have sweated in, but because of the natural ventilation, there should be a bit less sweat than with polyester. The fiber texture is also not as smooth as any synthetic, which is good news and bad news. The smooth surface of polyester yarn is an excellent host for microbial growth, and as the fibers move against each other, the microbes stay put. Wool fibers, however, have a scale structure that does not encourage the microbes, and as the fibers rub, they self-clean. More sensitive skin will be aware of this texture, however, especially as you warm up and your pores open.

The upshot of the anti-microbial nature of merino wool is that it is almost funkproof. As long as the garment is allowed to dry naturally (say, overnight), you can wear your merino baselayer many times before it smells like the bottom of a gym bag.

Synthetics do have the benefit of smoother texture, better wicking capacity and faster drying, but can be rather smelly if not washed promptly.

Price wise, in similar weights the merino will be more expensive, with the comment that you don't need to wash as often, so you can buy fewer pieces.

Different conditions call for different equipment, and base layer is probably the easiest clothing category to experiment with, becasue bringing extra along doesn't take up much space but can make a big difference in your comfort, confidence, and enjoyment of cold-weather activities.