I have been wearing the same pair of long underwear for three weeks. As a conversational icebreaker, that may not be an appealing admission. But since these are Icebreaker Bodyfit260 high-performance thermal leggings, it's an impressive claim—though hardly a competitive one: According to the New Zealand maker of the long- suffering long johns, the world record stands at 196 days between washings. To be fair, that was set by a solo adventurer in Antarctica and not in a small New York apartment under the watchful eye of my concerned wife.

I have jogged, flown coach between coasts, played 17 sets of tennis, cooked lasagna, and slept in my Bodyfit260s and I have to report that they remain remarkably comfortable and (wifely horror notwithstanding) not too offensive. Icebreaker is one of a few companies developing nonsynthetic sports wools, a less clingy, and thus less embarrassing, alternative to spandex. There's something wholesome but still excitingly futuristic about this stuff: It's durable, breathable, light, non-itchy, antimicrobial, sweat-wicking, UV-deflecting, and all-natural. The idea behind the Icebreaker line is appealingly simple: Start with thread spun from hearty merinos living at high altitudes (up to 7,000 feet) where temperatures fluctuate wildly between seasons. As the company's founder, Jeremy Moon, writes: "If the fiber didn't work, the animals would die every time it snowed. But it does and they don't."

I took a sampling of the new sports wools and put them through the paces of Extreme Real Life conditions. A retreat from synthetics, an urge to harness wool's natural protective powers—all of that sounded good to me. On the other hand, I've spent time on a Tasmanian sheep farm, and the image of those animals' coats after a long and dirty winter is not a pretty one. What's surprising about all the fabrics I tested is how light and smooth they are on the skin and how easily they shuttle between active and everyday uses.

Ibex Vertigo Jacket (www.ibexwear.com; $160)

Ibex, a 10-year-old company based in Woodstock, Vermont, sources its wool from New Zealand and Austria and makes, among much else, all-wool cycling gear. The raglan-sleeve Vertigo Jacket's loden is processed to protect the "natural lanolin in the fiber, making it more weather- and stain-resistant," according to the Web site. I found it had a soft but firm nubbiness and was pleasant to the touch, somewhere between a sweater and a jacket. An odd compliment for workout wear: It's cut nicely. I'd go jogging in it and realize I was still wearing it at dinner that evening. And I just checked: no stains.

SmartWool M Microweight (www.smartwool.com; $55)

Owned by Timberland, SmartWool is accomplished in the advanced-wool arena (they make many a sock). I wore the M Microweight Crew to dig ditches at a friend's house in Northern California (don't ask) and it kept me blessedly comfortable while I toiled in the afternoon sun and warm when evening came. As an added benefit, the safety shade of "Aspen" yellow added to the impression that I was part of a roadside crew. Unless you need to be visible from a quarter mile away, I'd suggest something more subtle.