How to Choose Wool Clothing

• Putting Wool to the Test
• Impressions from the Field
• Wool: A Brief Overview
• Wool: Then and Now
• What is Merino Wool?
• Merino Wool's Performance Characteristics
• Wool Q&A
• Brands Compared

Pop quiz: In which of the following situations should you avoid wearing wool? (Choose all that apply.)

• Cross-country skiing in mild spring conditions
• Alpine skiing
• Hiking on a warm, sunny day
• Trail running on a shadeless route in summer
• Fitness training, indoors or outdoors, year-round

Answer: None of the above.

Surprised? You're not alone. Personally, I would have never imagined wearing wool when I expected to work up a sustained sweat. Wool, as I perceived it, would be too hot, too bulky, too scratchy, just plain too old-school for most of the activities mentioned above.

That was until I was handed a soft, smooth T-shirt made from 100% "microweight" merino wool (more on this fiber later) and sent off to try it in the REI test kitchen—in this case, a section of the Pacific Crest Trail just south of the Canadian border during a very warm stretch of August weather. It was here that I learned first-hand about wool's performance characteristics.

Putting Wool to the Test

Over 3 days I hiked 47 miles. Being a dutiful 2-legged test module, I wore the same shirt all 3 days. Part of the final day was a 3-mile, uphill, shade-free grunt in the heat of the day.

The scenery? Far-reaching and dramatic. The weather? Roasty toasty. Even at 6,000 feet it was easily over 80°F (27°C) on the trail. On such a warm day, would a wool tee—solid black, no less—be too hot to handle?

And what about in chilly conditions? Just a week later I was in Mount Rainier National Park on a cloudy day when temperatures never reached 60°F (15°C) and fog hung low. Would the lightweight, long-sleeve wool tee I wore on that day be sufficient for a 7.6-mile hike with 2,500 feet of elevation gain?

Impressions from the Field

Hot conditions: My fears that I might bake like a potato inside a wool wrapper were unfounded. I did sweat a lot, which is typical for me during a hike. But much of the time the shirt's fabric seemed to dry reasonably quickly, particularly when exposed to moving air. For the majority of the trip, the shirt felt slightly damp rather than saturated. The exception was the ventilation-free zone where my back pressed into the pack.

Cool conditions: On both trips, moisture did not linger long in the shirt's fibers. Periodic cool breezes created no lasting chills. If anything, the lightweight wool felt reassuring and comfortable when the air felt cool. Maybe that was just my mind playing tricks on me, but I thought the shirt felt fine. On my foggy hike, when I paused for extended rest stops I was inclined to dig out an extra layer. But when active I felt comfortable.

Odor-retention: I perspired so much on my hot-weather trip that salt residue formed a number of white blotches that resembled reverse Rorschach ink blots on the shirt's black fabric. Yet after 3 days of continuous use the shirt's stink index was almost nonexistent. That may have been the biggest surprise the shirt delivered.

So, whaddaya know? I not only survived the experience, my first encounters with a wool tee during sweaty, aerobic activities proved to be positive.

I'm not claiming that merino wool is a miracle fiber. It will not whiten your teeth or keep you zestfully clean as you wear it. Nor am I going to toss my synthetics, which technically dry faster than wool. But the comfort and low-odor factor delivered by merino wool were genuine eye-openers for me.

Your own results with merino wool, of course, may vary. Yet customer reviews at REI.com are routinely enthusiastic for wool apparel, and I hear the same buzz from coworkers who claim a long-time allegiance to wool. Thus I encourage anyone who shares my initial skepticism toward wool to consider the merino version of the fiber.

Wool: A Brief Overview

Wool is a natural fiber composed primarily of keratin, a protein found also in hair, fingernails and animal hooves. Sheep serve as the primary source of wool. (A limited supply also comes from goats, alpaca, llamas and a few other animals.) Historians estimate that humans have used wool (for clothing, tapestries, bedding and carpeting) since 10,000 B.C.

Wool fiber—not quite hair, not exactly fur—grows in clumps referred to as staples. These staples are held together by grease and lanolin present in freshly shorn wool, creating the appearance of a thick, single blanket—a fleece. In contrast, human hairs fall to the floor individually by the hundreds during a haircut.

Wool's key characteristic is its fiber diameter, measured in microns. (A micron equals one millionth of a meter). Fiber diameter largely determines the quality (and price) of wool—and the smaller (finer) the diameter, the softer the wool's texture. Merino wool typically ranges between 15 to 24 microns, with anything below 17.5 microns considered "ultrafine" and well-suited to next-to-skin applications.

Wool fibers have 2 other noteworthy attributes:

1. Minute scales (resembling overlapping roof shingles, or a stack of ice cream cones, each with irregular, "nibbled" edges). These scales play a major role in wool's resistance to water. (Details appear later in this article.) In coarser grades of wool, these scales can contribute to the scratchiness people traditionally associate with wool.

2. A natural wave (tiny bends, crinkles or crimps) in the fiber. A high number of crimps per inch creates a soft sensation on human skin. Merino wool fibers typically have dozens of crimps per inch.

"Fine merino fibers bend when they contact the skin," says Dr. Simon Causer, the research and design manager for Christchurch-based New Zealand Merino Co. "They do not poke or irritate skin, so the feeling is one of softness rather than prickliness."

Wool garments exhibit excellent shape-retention of due to the crimp in the fibers. Crimping also creates countless tiny air pockets in fabric, capable of trapping air warmed by the body or buffering skin from hot external air. That may sound a little too good to be believed, but a wool base layer actually can help the wearer maintain a comfortable body temperature in either cool or warm conditions.

Wool: Then and Now

Wool has long been a classic choice for warmth. In 1953 Sir Edmund Hillary included some traditional wool items (tweed coat, a wool scarf) in his clothing mix during the first successful ascent of Mount Everest.

Synthetic fabrics—soft, light, with low bulk—gradually began to supplant wool among outdoor adventurers, a shift that dramatically accelerated when Polartec® introduced Polarfleece in 1979.

Fine-diameter merino wool is the modern-day comeback fiber of the wool category, delivering both a soft touch and technical performance attributes. Made-from-merino apparel aimed at outdoor types (designed by companies such as SmartWool, Ibex and Icebreaker) started appearing at REI in the late 1990s.

Despite lingering stereotypes about wool (and I confess I sustained them in my own mind; mea culpa!), merino wool choices, both in socks and apparel, are now widely available.

What is Merino Wool?

The source of merino wool is merino sheep, a breed that originated centuries ago in Spain. (The word "merino" has Spanish roots.)

Merino sheep were introduced to Australia in 1794, and they flourished in the island nation's temperate interior. Today the majority of merino sheep are raised in New Zealand (at high elevations), Australia, South Africa and South America where the climates and the vegetation consumed by sheep contribute to the exceptional quality of merino wool. It is estimated that 1 square inch of skin on a merino sheep produces roughly 4 times the number of fibers than other breeds.

As mentioned earlier, merino wool fibers range between 15 to 24 microns in diameter, with 17.5-micron fibers (rated "ultrafine") often used for next-to-skin apparel. The merino industry regards 18.5 microns as the average fiber diameter most people can wear without experiencing an itchy sensation.

In comparison, human hair ranges between 18 and 180 microns, with an average diameter of about 60 microns. Only the wispiest, most flaxen human hair comes close to approximating the diameter of merino wool.

The abundant crimps in merino wool fibers permits the spinning of high bulk, resilient yarns, which can then be knitted or woven into structures tailored to particular end uses. For outdoor apparel and socks, knits are the most common structures.

Merino Wool's Performance Characteristics

Merino Wool: Virtues by the Dozen

1. Warmth
2. But not too much warmth
3. Moisture management
4. Water-resistance
5. Odor-resistance
6. Flame-retardance
7. Durability
8. Stretch
9. Crease-resistance
10. UV light-resistance
11. Easy care
12. Sustainability

1. Warmth: With many crimps per inch, wool forms a countless number of almost microscopic air pockets in between individual fibers. While the overall fabric is breathable, these miniscule pockets trap body-warmed ("dead") air. As with sleeping-bag insulation, trapped air keeps a person warm.

What about damp conditions? A property unique to wool is its ability to release small amounts of heat as it absorbs water. This effect is known by the arcane term "heat of sorption." Energy, in the form of small amounts of heat, is produced through the work of moisture-absorption (and condensation) by wool fibers.

Interestingly, as noted in the next section, this effect is reversed as the fiber dries. Thus by absorbing and releasing controlled amounts of moisture and heat, merino wool buffers the body's microclimate in changing environmental conditions. This leads to manufacturer assertions that merino wool delivers "natural air conditioning" —a lofty claim, yet one that seems to have merit.

2. But not too much warmth (in other words, temperature control in changing conditions): Everyone associates wool with warmth. But can it really give a person the best of both worlds, providing comfort in both warm and cool conditions?

So it appears. (After all, sheep manage pretty well in warm weather, perhaps a survival attribute developed over centuries.) But wouldn't the body-warmed trapped air, which warms me when it's cool, cause me to overheat when it's hot? No, wool proponents tell me, because wool tends to work like an insulated mug:

• Wool fibers, while highly breathable, buffer skin from air heated by the sun the same way they can trap warmed air and keep it close to skin in cool conditions.
• By efficiently managing the humid microclimate created between skin and clothing (see details in the Moisture Management section below), wool keeps skin regulated for comfort in hot conditions.

Based on my anecdotal experience, I can't argue with those assessments.

3. Moisture management: Wool has the capacity to both absorb perspiration (in vapor form) while also resisting water (in a liquid state such as light rain). Admittedly, this is another of those you-can-have-it-both-ways claims that sounds too good to be true, but wool proponents insist they have the science to back it up.

While the exterior layer of a wool fiber is hydrophobic (water-resistant, that is; see next section for an explanation), its inner layer, its cortex, is hydrophilic (water-loving). The cortex can absorb about to one-third of its weight in moisture (estimates range from 27% to 36%), typically without feeling damp. It may, however, feel a few grams heavier in this condition.

On a perspiring person, in the high-humidity zone between fabric and skin, sweat in the form of vapor is absorbed by the wool fiber's cortex. Meanwhile, the hydrophobic exterior layer of the fiber next to your skin minimizes the chance that wet fabric will come in contact with your skin.

The moisture absorbed inside the cortex? It is impacted by air and sunlight on the outside of the garment. By being exposed to a lower-humidity zone, moisture is released through evaporation, and the fabric feels drier. The wearer thus feels comfortable.

Synthetic fabrics "wick" moisture by transporting it through very narrow air spaces between hydrophobic (water-avoiding) fibers. This requires sweat vapor to condense before it is moved through the fabric—an extra step, wool proponents assert, that makes synthetics slower than wool's moisture-management process.

4. Water-resistance: The scaly exterior layer of a wool fiber is called the cuticle and is overlaid with the epicuticle, itself coated with lanolin, a waxy, water-shedding film. The epicuticle and its waxy coating is what confers wool's resistance to mist and light rain. This structure also helps make the fiber resistant to stains, mildew and mold.

5. Odor-resistance: While the nuances of wicking efficiency between wool and synthetic fibers can be argued, few dispute the claim that wool apparel does a superior job of repelling odors.

After 3 days and 47 trail miles, I could pull off my merino wool tee, bury my nose in it and not pull away with my eyes spinning while I gasped for air. It didn't exactly smell fresh, but the stench factor was remarkably low. And as a hiker who has logged more than 9,000 trail miles, I know about stench factor.

6. Flame-retardance: Wool has a lower propensity for ignition, and burns with a lower heat release than all other common textile fibers. (The protein keratin does not support combustion.) While the application of a direct flame will initially cause some smoldering, it will not ignite a fire. When comparing wool and synthetic items, consider that wool fibers will not melt (or stick) when burned.

7. Durability: Wool fibers, even finer merino wool fibers, can accept repeated bending without breaking and is considered more durable than other natural fibers (cotton and silk). However, synthetic fabrics are believed to offer a higher test strength than wool. I find wool socks show signs of wear, particularly in the Achilles area, faster than synthetic socks.

8. Stretch: Owning to the crimped structure of the individual fibers and carefully designed yarn and knit structures, wool fabrics stretch relatively freely and thus won't inhibit movement. Wool garments routinely return to their original shapes after being stressed. And because wool fibers are adept at absorbing moisture, they exude a natural antistatic quality.

9. Crease-resistance: A wool tee shakes out the wrinkles fairly quickly after spending a few days crammed inside a pack. Wool is also well-known within the garment industry for its ability to retain creases where creases are desired, such as slacks.

10. UV light-resistance: Though wool garments are not routinely marketed with an ultraviolet protection factor (UPF) rating, the fabrics designed with merino wool fibers are considered a very satisfactory buffer against UV light.

11. Easy care: Machine washing is virtually universal in wool-based performance apparel. Most clothing items can also accept certain dryer cycles as well, though I line-dry my tee just to go easy on it. Check individual items for specific care instructions.

12. Sustainability: Some people simply prefer natural fibers over synthetics, which in some way use petrochemicals. Plus, no shortage of merino sheep exists. Flocks aplenty roam many parts of Australia and New Zealand (and elsewhere), cultivating the raw materials for a future assortment of performance-oriented activewear and insulation. Wool advocates also point out that wool, unlike synthetic materials, will also eventually decompose when its usefulness is exhausted.

Wool Q&A

Q: Does merino wool have any downside?

A: Some factors to consider:

• Shrinkage: Follow manufacturer laundering instructions faithfully. If hand-washing, line-drying or reduced heat when drying are recommended, take such guidance seriously. Traditional wool has a reputation for shrinking, and merino wool, inattentively treated, could experience a similar fate.

  Why is wool vulnerable to shrinkage? The scales of individual wool fibers, in the formation of stacked cones, migrate in a single direction—toward the root, especially when dipped in a slippery solution such as soap and water. An assortment of modern-day treatments, however, have greatly minimized (virtually eliminated, in fact) this risk.

• Special handling when laundering: As mentioned above, some wool garments require hand-washing or other delicate treatment. However, the clear majority of merino wool items offered at REI are machine washable, and many are dryer-friendly.

• Insects: Several specialized insect families (moths and carpet beetles) have evolved to be able to digest wool. (It is believed moths only in the larval stage actually eat wool.) However, these species are more readily attracted to wool in its raw from than as a finished product. Most wool products also contain an insect-resistant treatment to deter attack. Suggestions:
  • Wash or dry-clean wool items after all periods of extensive wear. Be especially vigilant when food spills are evident.
  • After cleaning and before storing for prolonged periods, place items in an air-tight plastic bag.
  • Moths dislike light, fresh air and regular laundering.
  • Want an old-school, chemical-free alternative to mothballs? Keep all woolens in a cedar-lined chest or closet.

• Cost: Wool items are on the pricey side. Converts, though, find wool's performance characteristics to be worth the cost.

• Humid conditions: Wool's ability to transfer water vapor from the humid microclimate close to the skin to the lower-humidity environment outside the garment may be compromised in very humid conditions. This would be true, of course, for any fiber or fabric.

Q: What other types of textiles use wool?

A: Many, including those associated with the more fashion-oriented side of the apparel trade (often woven in construction) or in carpet/rugs and bedding. Examples include flannels, felts, worsteds, gabardine worsted and tweeds. Cashmere is perhaps the most luxurious wool.

Q: Is alpaca wool used in performance apparel for the outdoors?

A: Alpaca fiber is getting a look by some designers. The alpaca is a relative of the llama. Alpaca fiber is actual hair—long, fine and smooth. It features dense, abundantly crimped fibers, a soft texture and tremendous insulation value at a very low weight.

Brands Compared

So, what's the difference between brands? Is all merino wool apparel created equal? Not necessarily. Assuming the same quality of fiber stock, the key to high quality lies in the quality of the spun yarn and the quality of the fabric produced. This can be influenced by machine settings and a host of other factors.

In finished products, such nuances are difficult for an untrained eye to detect. Sage shoppers are usually rewarded for sticking with established brands that have cultivated a reputation for creating quality products. You might find it useful to study some of the product reviews of wool apparel (presented on individual product pages) at REI.com.

We invited representatives of a number of brands carried at REI and REI.com to offer their point of view on what makes their version of merino wool apparel stand out.

The brands are presented alphabetically, and each representative was requested to make his or her case in 250 words or less.

Comments from Ibex

Wool leaders?

Truth is, we didn't set out to be the leaders of anything. We just chose wool because we believe it works better. But then a funny thing happened: We started to learn all sorts of stuff from sheep. We learned how wool is great, why it's great, how it gets from the dirty, greasy mess it is when it's shorn to the superfine wonder fiber you wear on your back. (Hint: there are a lot of people along the way who help make Ibex wool the beautiful thing it is). In a way, we discovered wool's amazing qualities right along with everyone else. We don't think of ourselves as leaders. We think of ourselves as devoted to something we believe in.

So where does it all start? It starts with the sheep and the farmers. A sheep farmer is like a vintner, handling most of the real work before shearing time ever really rolls around. They select the right kind of sheep, raise them in the right environment, and look after their health and diet in the right way. All of which leads the sheep, step-by-step, to the creation of just the right kind of fineness and weight in wool fiber for just the right purpose.

Because great wool isn't just grown—it's crafted.

—Keith Anderson, Ibex Marketing

Comments from Icebreaker

Icebreaker merino from New Zealand is a natural miracle fiber that offers the ultimate in temperature regulation and breathability. Icebreaker uses pure merino, hand-picked from 120 high-country ranches in New Zealand to create edgy outdoor clothing that combines nature's work with human technology and design.

Every Icebreaker garment contains a unique Icebreaker "Baacode" which means you can trace the origin of your garment back to the merino sheep ranch it was grown on (see www.icebreaker.com/baacode). Your unique Baacode will let you see the living conditions of the high country sheep that produced the merino fiber in your Icebreaker garment, meet the farmers who are custodians of this astonishing landscape, and follow every step of the supply chain.

Icebreaker merino is much finer than traditional wool. It's silky soft to touch, insulates much better, breathes more effectively and doesn't hold odor. Merino is a complex protein-based fiber mad from keratin. Keratin is the same constituent protein that is found in our skin, hair and nails. It's natural and renewable, so it's hardly surprising that it feels so good next to your skin.

Icebreaker merino's natural antibacterial properties also enable garments to be worn for several days without washing. It's machine washable and dries in a flash—making it perfect for traveling light.

Your Icebreaker garments can be worn solo or layered with other Icebreaker pieces to create a fine, breathable system that moves effortlessly between the mountains, trails, water and the city, or where ever your travels take you.

—Deb Boswell, Icebreaker U.S. Marketing Manager

Comments from SmartWool

At SmartWool, we've been tickling the soles of troubled toes since 1994. When we're not comforting people from their toes on up, or outside playing, we're thinking up ways to comfort their inner souls.

We want to be a company you feel good about—from the best products to the best business practices. Our decisions are driven by what's right for the world, not by what the "suits" tell us . . . unless, of course, they're wearing head-to-toe SmartWool!

We helped develop and then became the first Merino wool company to adopt the world's first wool accreditation program, Zque, assuring you our wool is produced using best management practices from start to finish.

Ten percent of smartwool.com sales go to the SmartWool Advocacy Fund and then to nonprofit organizations who share our passion in making the world a better place. For SmartWool Pink Ribbon socks sales, 2% is donated to the SmartWool Breast Cancer Fund.

We think globally and act locally. We have received numerous local business awards including Philanthropic Business of the Year, PACE certification and a Gold Level Sustainable Businesses certification.

We donated 1,000 volunteer hours to local non-profit organizations and our offices close twice a year for a little hometown park TLC.

SmartWool has two employee-driven corporate sustainability teams whose goal is to reduce annual energy and water usage by 20% and waste by 50%.

And that's just the beginning. Who knew something that felt so good on your toes could feel so good for your soul? We did!

—Molly Cuffe, SmartWool Communications

Technical contributors and consultants: Dr. Simon Causer, Research and Development Manager, New Zealand Merino Company; Dr. Alan Donaldson, Professor Emeritus, North Carolina State University College of Textiles; Kimbal Curtis, Senior Research Officer, Dept. of Agriculture, Western Australia.