Why 17.5 microns
The number on the label that actually tells you something about the wool.
A human hair is about 70 microns thick. A strand of Icebreaker's standard merino is 18.5. Ours is 17.5. A one-micron difference sounds like nothing. It's the difference between a base layer you'd wear and one you'd return.
What the number measures
Micron count (μ) is the average fibre diameter, measured by laser or airflow on a sample of raw fleece. The lower the number, the finer the fibre. The finer the fibre, the softer it sits against skin and the less it wants to itch.
Merino sits between 15 and 24 microns. For context:
- Superfine: 15 to 17.5. Rare. Expensive. Used in Loro Piana suits.
- Ultrafine: 17.5 to 19.5. What we use.
- Fine: 19.5 to 22. Most "merino" base layers on the market.
- Medium: 22 to 24. Crossbred and commodity wool.
Anything over 22μ and your skin starts to notice.
Why it matters for a base layer
A base layer sits against bare skin for the whole day. Pilling, itch, scratch — any of that becomes a reason you stop wearing the garment. The single biggest predictor of whether people wear their merino once or wear it forever is how it feels in the first thirty seconds.
17.5μ feels like cotton. 18.5μ feels like cotton if you're paying attention. 20μ feels like wool.
Where 17.5 micron wool comes from
Fibre diameter is set by breeding and by conditions. Merino sheep grazed in hard country — cold winters, dry air, high altitude — produce finer fibre than the same breed at a lowland station. The South Island high country is one of the few places on earth where 17.5μ is achievable at scale.
Our wool comes from three stations in the Mackenzie Basin, Waitaki, and Central Otago. It takes about five sheep to make one Long Jon.
What the number doesn't tell you
Micron is necessary, not sufficient. It says nothing about staple length (how long each fibre is, which affects durability), yield (how much usable fibre you get per fleece), or lanolin content (how self-cleaning the fabric is). The number on our label is 17.5. The specs behind it are on every hangtag.
Don't trust a merino brand that doesn't publish their micron number.
That's most of what you need to know. The rest is the wool doing the work.