Micron is the measure of fibre diameter of wool (one micron is one one-thousandth of a millimetre). Standard Deviation is a statistic that summarises the way diameter results from individual fibres are spread around the mean fibre diameter. It measures the absolute distribution of fibre diameter either side of the Mean and is expressed in microns. Sixty eight percent (68%) of fibres fall within a range one Standard Deviation either side of the Mean, and 95% of fibres fall within a range two Standard Deviations either side of the Mean. For example, a wool with a Mean Fibre Diameter of 20µm and a Standard Deviation of 4µm will have 68% of fibre snippets between 16.0µm and 24.0µm and 95% of fibre snippets between 12.0µm and 28.0µm. Coefficient of Variation is a measure of the relative distribution of fibre diameter and is expressed as a percentage (%). It is calculated by expressing the standard deviation as a percentage of the Mean. For example, a wool with a Mean Fibre Diameter of 20µm and a Standard Deviation of 4µm will have a Coefficient of Variation of (4.0÷20.0) x 100=20%. Comfort Factor is expressed as a percentage and is defined as the proportion of fibres which have a diameter of less than 30µm. Research has shown that wools with a comfort factor of 95% or greater (i.e. less than 5% of fibres greater than 30µm) can be comfortably worn against the skin. A wool with a comfort factor of 100% contains no fibres greater than 30µm. Spinning Fineness is expressed in microns and provides an estimate of the performance of the wool when it is spun into yarn. The spinning fineness is calculated from the measured Mean Fibre Diameter and the measured Coefficient of Variation of Fibre Diameter. The spinning fineness is the same as the Fibre Diameter when the Coefficient of Variation (CV) is 24%. Wools with a CV of less than 24% will have a spinning fineness less than the Fibre Diameter.
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