Traditional woollen school jumpers had a reputation for itchiness and yet Australian Merino is sought after by catwalk designers for its silk-like softness. The CSIRO has identified that the disparity can be explained by a comparison of fibre diameters.
Many wool fibres will have a diameter of 28µm or higher while diameters for Merino are generally around 22µm and extra-fine Merino must be 19.5µm or lower.
Proven in testing
The thesis that the superior softness of Merino is due to the fineness of its fibres was confirmed by CSIRO testing in which schoolchildren were given sweaters to wear made from wool fibres of varying diameters.
Children were chosen because their skin is softer than adults and more sensitive to subtle changes in texture.
In the trials, the fibre diameter of the sweaters was decreased gradually in steps from 25µm to under 20µm and the reactions of the schoolchildren recorded. (Fig 2)
At an average fibre diameter of 24.5µm, only 20% of the children felt the sweater was comfortable.
However, by dropping the average fibre diameter just 2 microns to 22.5µm, fully 70% of the children now found the garment to be comfortable.
By dropping the fibre diameter another 2 microns to 20.5µm even the most sensitive 10% of children found no discomfort whatsoever.
While these tests prove conclusively that it is the superior fineness of the Merino fibre that makes it so soft, the actual fibre diameters that are considered comfortable are purely indicative.
Variance from average diameters
The fibre diameter necessary to achieve next-to-skin softness also depends on the spread of fibre diameters.
The fibre diameter quoted for a wool bale is only the average and there will be fibres both finer and coarser present to varying degrees.
While wool with an average fibre diameter of 20.5µm would appear to provide unanimous comfort, the presence of a significant number of coarser fibres could significantly affect wearer comfort. AWI and the wider wool industry now recognise the importance of limiting the range of fibre diameters, and have instituted programs to produce greater uniformity in processing.
Effect of Finishing
A further factor that influences the choice of fibre diameter is the finish of the garment.
While a fibre diameter of 22.5µm might be necessary to achieve comfort in a certain sweater, a more bulky construction might allow the use of a slightly coarser diameter fibre. The general rule is that for garments with a smoother finish, a Merino with a lower micron count will be preferable.
For advice on the choice of Merino fibre diameters for particular garments, please contact Australian Wool Innovation.
Summary
Australian Merino is softer than traditional wool because its fibres are much finer. In choosing the appropriate fibre diameter to achieve next-to-skin comfort, consideration must be given to the spread of fibre diameters and the finish of the fabric, with smoother textures requiring a lower micron count.
Source
- Naylor, G., Phillips, D., “Skin comfort no longer a prickly subject”, CSIRO.
All figs and tables courtesy of CSIRO unless otherwise noted.
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