Micron vs Super Number: What the "Super" Label Actually Measures
Quick answer: Micron is a direct measurement of wool fiber diameter, while the Super number is an industry classification derived from that measurement—finer fibers earn higher Super numbers.
A lot of buyers treat "Super 130s" the way they'd treat a star rating — a single number that sums up how good the cloth is. I understand the instinct, but it's not quite right, and it's worth untangling, because the actual relationship between micron and Super number tells you something more useful than a star rating ever could.
Micron: The Actual Physical Measurement
A micron is a unit of length — one millionth of a metre — and in wool, it measures one specific thing: the diameter of the individual fiber. It's measured directly, typically by passing a sample through specialized optical or laser equipment that reads fiber thickness across thousands of individual strands and averages the result. Nothing about micron is a judgment call. It's a physical fact about the raw material, the same way a diamond's carat weight is a physical fact rather than an opinion.
Super Number: The Classification Built On Top
The Super number is what the trade built on top of that raw measurement, so buyers and mills could talk about fineness without reciting decimal micron figures constantly. It follows the IWTO "Super S" Code of Practice, which sets a maximum mean fiber diameter for each Super tier. Super 100s tops out at 18.75 microns, Super 120s at 17.75, Super 150s at 16.25, and Super 180s at 14.75 — each step of ten in the Super number corresponds to a 0.5 micron drop in maximum fiber diameter. So a higher Super number always means a finer fiber. That part of the system is genuinely reliable.
When the Label and the Fiber Don't Quite Match
Here's the part worth being honest about. The Super classification depends on the fiber genuinely meeting that micron threshold, and across a global supply chain with many hands involved, claims aren't always independently verified at every single step before they reach a buyer. This isn't a scandal specific to any one supplier — it's a structural reality of any industry where a number on a label depends on measurements taken further up the chain.
The practical response isn't suspicion, it's verification. If a Super number matters to your decision — and for a significant purchase, it should — ask your supplier for the actual micron figure behind the claim, not just the Super label. A supplier confident in their fiber will have that data and share it without hesitation. Cross-referencing the micron number against the Super classification takes thirty seconds and tells you whether the two actually line up.
Micron Isn't the Whole Story Either
Even a verified micron figure only tells you about fiber fineness — it says nothing about how that fiber was spun. As we covered in Worsted vs Woolen, the same fine fiber can be combed and tightly spun into something crisp and structured, or carded and loosely spun into something soft and textured. And as we cover in Two-Ply vs Single-Ply, whether that yarn is twisted once or twice changes strength and drape again. Fineness, spinning method, and ply are three separate variables that stack together — no single number, Super or otherwise, captures the full picture on its own.
Micron vs Super Number at a Glance
| Micron | Super Number | |
|---|---|---|
| What it measures | Fiber diameter directly | A classification derived from micron |
| How it's obtained | Direct optical/laser measurement | Assigned based on the IWTO Super S table |
| What it tells you | Precise physical fineness | A trade-standard fineness tier |
| What it doesn't tell you | Spinning method, ply, durability | The exact micron figure, or how the yarn was spun |
Going forward, our product descriptions will list both the micron figure and the Super number together wherever we have it, rather than the Super number alone. It's a small change, but it means you're never taking a label's word for it — you can check the math yourself.
FAQ
Is a higher Super number always better? Not automatically. A higher Super number means a finer fiber, but finer fibers can also be more delicate. The right choice depends on how the fabric will be used and how it was spun, not the Super number in isolation.
How can I verify a Super number claim? Ask the supplier for the actual micron figure behind the claim and check it against the IWTO Super S table yourself. A confident supplier will have that data on hand.
What's the relationship between micron and softness? Generally, a lower micron means a finer fiber, and finer fibers usually feel softer against the skin. But softness also depends on the spinning method and finishing, so micron alone doesn't guarantee a specific hand-feel.
By Daniel Hui, Founder, Yoo's Club
