Merino Wool Glossary

Wool has more jargon than it needs. Here is what the terms actually mean.

Term	What it means
Micron	Average fiber diameter, in thousandths of a millimetre. Lower is finer. Below about 22, most people stop feeling prickle.
GSM	Grams per square metre. How heavy the fabric is. About 150 is lightweight, 200 midweight, 250 and up heavyweight.
Ounce weight	The same measurement in imperial units, ounces per square yard. One ounce is about 34 gsm, so a 4 oz jersey is roughly 135 gsm.
Merino	A breed of sheep with an unusually fine fleece, and by extension the wool from it.
Superfine	An informal grade, generally meaning merino under about 19.5 micron. Not a certified standard, so treat it as a description rather than a guarantee.
Worsted spun	Yarn made from fibers combed parallel before spinning. Smoother, stronger, pills less. Slower and costlier to produce.
Woolen spun	Yarn made from fibers left jumbled. Loftier and warmer for its weight, but fuzzier and quicker to pill.
Jersey knit	The basic single-layer knit used for most t-shirts and base layers. Stretches, drapes, lies flat.
Next to skin	Fine enough to wear directly against the body rather than over another layer.
Base layer	The first layer you put on. Its job is moisture and temperature management, not insulation on its own.
Pilling	Small balls of fiber that form where fabric rubs. Shorter fibers and woolen spun yarns pill more. Some pilling on any new knit is normal and settles down.
Lanolin	The natural wax in raw wool. Mostly removed during scouring. A small number of people are sensitive to it, which is different from prickle.
Scouring	Washing raw fleece to remove grease, dirt and vegetable matter before spinning.
Superwash	A treatment that coats or removes the fiber's scales so it can be machine washed without felting. Convenient, and it involves a resin coating that some buyers would rather avoid.
Felting	What happens when wool meets heat, moisture and agitation together. The scales lock and the fabric shrinks irreversibly. This is what people mean when they say wool shrank.
Mulesing	A surgical practice used on some sheep to prevent flystrike. Widely criticised on welfare grounds. Non-mulesed sourcing is a meaningful claim worth looking for.
RWS	Responsible Wool Standard. A third-party certification covering animal welfare and land management.
Corespun	Yarn with a synthetic filament core wrapped in wool. Stronger and longer wearing, but no longer 100% wool.
Wicking	Moving moisture away from the skin. Wool does this as vapor before the moisture becomes liquid, which is why it can feel dry when a synthetic feels clammy.

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