Merino wool, decoded: what the micron numbers mean and when it's worth the money
Merino appears on everything from $25 tees to $300 sweaters with no explanation of what separates them. The answer is one number: the micron count. Here is how to read it.
What a micron count tells you
The micron is the fiber's diameter. Lower means finer, softer, and more expensive. Human itch perception kicks in around 30 microns, which is why traditional wool (30-40 microns) scratches. Merino runs 24 down to 11.5: 20-24 microns is rugged merino (base layers, hiking socks - durable, mildly textured). 17.5-19.5 is the sweet spot for next-to-skin knits you will actually wear weekly. 15.5-17 is luxury territory - indistinguishable from cashmere to most hands. Below 15 (ultrafine) is where prices jump faster than the feel improves.
Why merino behaves differently
Three properties do the work. The fiber's crimp traps air, so it insulates at a third of the bulk of cotton. It absorbs up to 30% of its weight in moisture vapor before feeling wet, which is why a merino tee survives a commute that kills cotton. And the fiber's surface resists odor-causing bacteria - the reason travelers wear one merino shirt for days.
Merino vs the alternatives
Against cotton: merino wins on warmth-to-weight, odor, and drape; cotton wins on price, durability at high abrasion, and washability (merino wants gentle cycles and flat drying). Against cashmere: cashmere is softer per micron but pills faster and wears through at elbows; merino at 17.5 is 90% of the feel at half the price and twice the lifespan. Against synthetic base layers: synthetics dry faster and cost less, but hold odor permanently after a year; merino doesn't.
The buying checklist
Look for the micron count on the label or product page - a brand that won't publish it is usually selling 21+ micron wool at 17.5 prices. Check the knit gauge: fine, dense knits pill less than loose, lofty ones. And prefer 100% merino for base layers, but accept a 10-20% nylon core-spun blend in socks and high-wear knits - it doubles abrasion life for a barely detectable feel change.
The honest verdict
Merino is worth the premium in exactly three slots: base layers, travel knits, and socks. For a chunky winter sweater that never touches skin, regular lambswool at half the price does the same job. Spend where the fiber touches you.