Wool, Measured in Microns
Wool, Measured in Microns
Wool does not itch because it is wool. It itches because of a number.
People say they cannot wear wool. Almost none of them are right. A true allergy to lanolin is rare. What nearly everyone is reacting to is fiber diameter, and that is measurable.
What a Micron Is
A micron is one thousandth of a millimeter. It is the unit used for the diameter of a single wool fiber.
For scale, a human hair runs roughly 60 to 80 microns. Silk is around 10 to 13. Cashmere averages about 14 to 19. Merino runs roughly 15 to 24. Lambswool sits around 24 to 30. Shetland spans about 20 to 28 at its finer grades. Coarse breeds go well past 30.
The Prickle Threshold
The itch is mechanical, not chemical. A fine fiber bends when it meets skin. A thick one does not. It stays rigid and presses into the nerve endings, and your skin reads that as prickle.
The threshold sits somewhere around 25 to 30 microns for most people. The trade measures what it calls comfort factor, the percentage of fibers in a sample finer than 30 microns. Once about five percent of the fibers are coarser than that, most wearers will call the cloth scratchy.
This is why the average number alone does not settle it. A yarn with a low average but a wide spread can still have enough coarse ends to prickle.
Fine Is Not the Same as Better
This is the part that gets lost. Superfine merino is soft, and it also abrades faster, precisely because the fibers are thin.
Wool above about 24 microns has body, resilience, and stitch definition that fine merino cannot produce. It holds a shoulder line. It survives. It felts properly. Medium and coarse wool is not a lesser fiber. It is a different one, chosen for the jobs that punish softness.
Staple length and crimp matter as much as diameter. A slightly coarser fiber with good length spins into a stronger, longer lasting yarn than a fine short one.
Which Is Why Tweed Is What It Is
A tweed is not trying to feel like a base layer. It is trying to hold a shape in weather for thirty years, and that calls for a fiber with structure.
Each year three Harris Tweeds are woven for us in Scotland, and three jackets are made from them. That cloth is protected by an Act of Parliament, which is a story of its own.
Buying by the Number
Anything worn against bare skin wants to be under about 20 microns. Anything worn over a layer can go coarser and will usually last longer for it.
And if a wool piece feels harsh in the shop, ask what the fiber is before deciding wool is not for you. It is almost always the grade, not the animal.
A Way Of Life.
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the Harris Tweed Psychedelic BLUE Tartan Western Jacket
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Harris Tweed: The Only Cloth Protected by an Act of Parliament