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Gear School: Merino Wool

This all-natural wonder fabric keeps you warm, cool, and stink-free.

Cold Day/Hot Day | Shop/Use/Maintain

Cold Day

Wool absorbs sweat vapor and releases it on the other side, preventing clamminess. With synthetics, sweat must recondense before the fabric can wick it away.

Each wool fiber has crimps (bends or crinkles). This wave creates millions of tiny air pockets, which, in the cold, store body heat, keeping you insulated even when the fabric is damp.

Hot Day

As sweat evaporates from your skin (like steam from a kettle), it cools the skin and nearby air. Wool’s micropockets trap this chilled air, buffering you from searing ambient temps.

The fiber’s core is hydrophilic and can absorb one-third its weight in water. The waxy outside is hydrophobic. So wool sucks up H20, but still feels dry on skin.

Scales, stacked like cones, cover the fibers. Warm, soapy water causes them to slide to the root and interlock—hence, shrinkage. But modern factory prewashes smooth the fiber, so it doesn’t shrink.


>> Types of wool Different breeds of sheep produce wool fibers of varying thickness. The finer the fiber, the softer the wool (and the pricier, due to prime animal stock, care, and knitting techniques). Historically, sweaters were woven from thick fibers—about 32 µm (microns)—that while warm, were scratchy, bulky, and shrink-prone. But in the 1990s, performance-wear companies started using wool shorn from merino sheep (raised mostly in New Zealand and Australia), which create fleece 15 to 24 microns wide; human hair is 80 microns, on average.

>> More than socks The finest fibers (<17.5 µm) are the gold standard for next-to-skin layers like shirts, long johns, and boxers. These high-end baselayers typically have a low weight of 150 grams per square meter, for a light, airy fit. Wider fibers (up to 22 µm) are usually found in midweight tops, outers, and socks. Check the tag for diameter and weight, and see how it feels against your skin.

>> Wool or synthetics? The latter tend to be cheaper and lighter, and dry faster. But merino fights odor, and feels warmer and less clammy when damp, so base your selection on personal preference. Wool is also natural, renewable, and biodegradable and can be produced using less petroleum and fewer toxic chemicals. >> Certification check When sheep are raised in a stressful environment (high animal density, low food quality, or mistreatment), their fleece fibers weaken, yielding garments prone to pilling and ripping. Look for Zque on the label; this New Zealand program accredits wool (from companies like Icebreaker, Ibex, and SmartWool) as being humanely made and environmentally, socially, and economically sustainable.


>> Cold and hot conditions Wool acts like a thermos, keeping you warm on chilly days and cool on scorchers.

>> Odor control Since the wool fiber’s core absorbs water and its hydrophobic exterior repels it, there’s no moist surface for microbes to grow on, making wool naturally antibacterial. So you can wear it for days without developing the arresting bouquet that can plague synthetics.


>> Wash You can machine-wash most merino garments. Follow care instructions, but in general, use a delicate cycle, with cold to warm water and mild detergents like Ivory Snow, Nikwax Wool Wash, or ones labeled “Free” or “Clear.” Never use chlorine bleach, fabric softener, or dryer sheets, or mingle wool with Velcro or barbs (like bras). Turn the garments inside out to avoid abrasion or color loss. Air-dry flat, though you can often toss socks and long johns into the dryer on low heat.

>> Fix
Field-patch holes with duct tape to prevent unraveling; darn later.

>> Stow
Wash first, as stains attract insects, then put in a tub. Merino is treated with a moth-repelling enzyme, so no need for mothballs.

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