I've been evaluating a base layer (the clothing worn next to the skin) made of merino wool. For those of you who don't like wool because it's too "itchy" and rough against the skin, this would be perfect. Merino wool has very fine fibers that are crimped so that when they are woven together into cloth they trap more air. It's the trapped air in the fabric that creates the insulation to keep your body at a comfortable temperature. The fine merino fibers do not itch the skin at all. In fact, the material feels downright silky…so much so that you might doubt that the stuff is wool. It's delightful to wear.
One of the nice things is that these articles of clothing can be washed like any other clothes. However, it is recommended that they be hung up to dry, rather than putting them in a hot clothes drier. But that's no big deal, because merino wool dries quickly. In fact, that's one of the great characteristics of this material — when you wear it, it retains its insulation properties even when it gets wet, and then it dries fast.
In my opinion, merino wool is the only natural fiber that should be worn as a base layer in an outdoor setting. Cotton (the other natural fiber) is horrible when it gets wet. It's like wearing a sponge that refuses to wring out. Wearing wet cotton is an invitation to hypothermia — it's like saying, "come and get me." Wool, on the other hand, keeps insulating and wicks the moisture away from the body, and dries quickly.
One of the arguments for cotton is that it is comfortable to wear in warm weather when it is dry. And most folks think wool is hot, so it wouldn't be comfortable in warm weather. Well, before you believe that, I suggest you compare the materials in the real world. My experience with merino wool makes me believe that, even on a warm day, I prefer the wool.
No question about it, the drawback to merino wool is its cost. If this fabric were as cheap as cotton, nobody would wear cotton. While cotton balls are cheap to grow, a Merino sheep is another story. This type of sheep was bred specifically for its soft, fine wool, and it is more expensive to produce than cotton or synthetics. But honestly, it's worth it to own a couple of shirts and pants made of this material. We bought ours from www.campmor.com at very reasonable prices, but you can find merino wool clothing at REI and other outlets as well.
One side note about fabric's role in survival — I was researching survival of aircraft wrecks and the fire that sometimes engulfs an airplane after a crash landing. It turns out that the kind of clothing you're wearing can sometimes mean the difference between making it out alive or burning to death. Synthetics catch fire and melt to the skin. Cotton burns much less aggressively, and wool is the most protective of all the fabrics that people normally wear. Unless you're a firefighter wearing Nomex, wool is your best protection. Something to think about.
Merino wool is excellent as a foundation for your outdoor clothing. Consider it your first layer of shelter from the elements.