Micron
Also searched as: micrometer, micrometre, µm, μm, fiber diameter
One micrometer. Often used to describe fiber diameter, but not a complete quality score.
In detail
A micron is one micrometer, equal to one millionth of a meter. It is commonly used for wool fiber diameter. A stated mean diameter summarizes a population of fibers rather than asserting that every fiber in the sample measures exactly that amount.
The science and numbers
Wool diameter is measured by methods recognized by the International Wool Textile Organisation (IWTO), which lists five. The projection microscope (IWTO-8) is the reference: fiber snippets are projected at 500 times magnification and measured one by one, which also allows the percentage of medullated fibers to be counted. Airflow methods (IWTO-28 for raw-wool core samples, IWTO-6 for combed sliver) infer a mean indirectly from how a compressed plug of fibers resists the passage of air, and are calibrated against the projection microscope. The Sirolan-Laserscan (IWTO-12, also ASTM D6466) and the Optical Fibre Diameter Analyser, OFDA (IWTO-47), measure large numbers of individual snippets optically and report the distribution as well as the mean. Because the methods sample and weight fibers differently, airflow and image-based results for the same lot can show systematic differences, so lots should be compared on the same method.
A practical example
For scale, 20 microns equals 0.020 millimeters. If comparing two wool lots, ask whether their numbers were measured on comparable samples and whether information about variability accompanies the average. This makes the comparison more useful than reading the number as a product grade.
What to distinguish
Diameter is different from fiber length, yarn linear density and fabric weight. A lower mean diameter alone cannot describe strength, pilling, origin or the performance of a completed garment.
Origins and history
The projection microscope, using instruments such as the WIRA microscope and the Lanameter calibrated with a graticule, became the reference method against which faster techniques were calibrated. The airflow instrument was extended to raw wool when IWTO accepted test method IWTO-28 in 1971, allowing mean diameter of sale lots to be certified from core samples. In 1995 IWTO accepted both the Laserscan (IWTO-12) and OFDA (IWTO-47) methods for raw wool and top certification, which made routine reporting of diameter variability practical alongside the mean micron figure.
Related terms
Sources & further reading
- Woolmark: What is the wool fibre?
- SGS Wool Testing Services: Airflow, OFDA and Laserscan (Info Bulletin 3.3B)
- Woolwise: Notes, Topic 7, Fibre diameter
- International Wool Textile Organisation: Test Method IWTO-47-2013
- ASTM D6466: Diameter of wool and other animal fibers by Sirolan-Laserscan
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.