Traps air in crimped animal fiber, so it warms you even damp and springs back from creases.
Also called: merino, wool blend, lambswool
The basics
What to know about wool
Wool is the fleece of sheep, a protein fiber built from keratin, the same material as your hair and nails. Each strand grows with a natural wave called crimp, and crimp holds still air between fibers, which is where the warmth actually comes from. Fineness decides comfort and is measured in microns, thousandths of a millimeter. Below about 20 microns wool feels soft against skin. Past 30 microns it triggers the prickle people call itch. Merino runs 17 to 22 microns and can be worn next to the body, while a coat tweed at 28 microns cannot.
Moisture behavior sets wool apart from every plant fiber. Wool absorbs up to 30 percent of its own weight in water vapor before feeling wet. It keeps insulating while damp, which is why it beats cotton on a cold rainy day. Odor also builds slowly on the fiber surface, so a merino tee goes three or four wears between washes. Creases relax overnight on a hanger in a steamy bathroom without an iron ever touching it.
Heat, water and movement together are what destroy wool. The fiber surface carries overlapping scales; hot water lifts them and tumbling locks them into one another. The garment shrinks and hardens for good. That is felting, and nothing reverses it. Wash at 30 C or below on a wool cycle, press the water out instead of wringing, and dry flat. Machine washable wool has had those scales coated or stripped at the mill, which softens the hand slightly.
Store it clean and sealed. Moth larvae eat keratin, and sweat and food traces draw them in. The sweater put away dirty in April is the one that comes out holed in October.
In photos
Wool on real products
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Sheep are shorn once a year and the fleece grows back, so wool is a renewable crop rather than a single harvest. Raw fleece is scoured in hot water and detergent to strip grease, dirt and plant matter. The grease itself is lanolin, which is refined and sold on into skin creams.
Clean fiber is then carded, a process that pulls it into a loose parallel web. Finer yarns are also combed, which removes short fibers and lays the rest straight. Combed and spun tight, the result is worsted yarn: smooth, strong and used for suiting. Carded only and spun loose, it becomes woolen yarn: hairy, lofty and used for tweeds and chunky knits. Lambswool comes from a sheep's first shearing, where the fiber tips are finer and softer than on later clips.
Best for
When it works well
Cold damp climates suit it above any other fiber, because wool keeps insulating after it takes on moisture.
Suits and tailoring rely on it, since the fiber springs back and holds a pressed line that cotton loses by noon.
Travel packing works well, as odor resistance stretches a merino layer to three or four wears between washes.
Households that never iron benefit, because hanging wool in a steamy room drops most creases out on its own.
Fire safety favors it, as wool chars and self extinguishes rather than melting onto skin the way polyester does.
