Not a true unit of measure, S or super S number is an index of the
fineness of the wool fiber and is
most commonly seen as a label on wool apparel, wool fabric, and yarn.
An S number on the label of a wool suit, or other
tailored wool apparel, indicates the fineness of the wool fiber used in
the making of the apparel. The numbers may also be found on wool fabric
and yarn. The S numbers for fine wool products are intended to
state, with precision, the fineness of the wool fiber used in the
product, as measured in micrometres.
The micrometre or micrometer, also commonly
known as a micron, is an SI derived unit of length equaling 1×10−6 of a
metre (SI standard prefix "micro-" = 10−6); that is, one millionth of a
metre (or one thousandth of a millimetre, 0.001 mm, or about 0.000039
Fiber fineness is one of the factors determining the quality and
performance of a wool product. In recent years it has also become an
important marketing device used by many mills, garment makers, and
retailers. The S number appears as a plural with an " s " or " 's "
following the number, such as 100s or 100's.
worsted count was only a rough measurement and has been replaced by
more exact methods such as the metric yarn count. However, for fine
wool, the memory of the older system survives in the S numbers which
have a very rough correspondence to worsted count. In other words, fiber
that yielded about 80 worsted hanks is roughly comparable to fiber
designated as 80s using the S numbers. The critical difference is that
while the worsted number was an indirect measure (and a rough one at
that) of yarn thickness, the S number is a direct (and precise)
measurement of the thickness of the fiber. The S number of fiber, and
hence of yarn, fabric, or garments made of that fiber, is determined
using the international standard promulgated by the International Wool
The International Wool Textile
Organisation (IWTO) is the promulgator of the Fabric Labelling Code
of Practice which governs the use of the "S" and "Super S" designations
for fine wool and wool blend fabrics. The Code defines the S number by
correlation to maximum fiber diameter. For example, 80s must have
maximum fiber diameter of 19.75 micrometres or finer and 90s, 19.25
micrometres or finer. This scale continues to the 210s at 13.25
micrometre or finer. Thus each step of ten (as from 80s to 90s or 90s to
100s) corresponds to 0.5 micrometre less in allowed maximum fiber
diameter. It has been proposed to extend the scale to 250s at 11.25
micrometre or finer.
Additional reference for wool measurements:
A micron (micrometre) is the measurement used to
express the diameter of wool fibre. Fine wool fibers have low micron
value. Fibre diameter is the most important characteristic of wool in
determining its greasy value.
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