Rieter

Specification of fineness

Index

With the exception of wool and hair fibers, fiber fineness cannot be specified by reference to diameter as in the case of steel wire, because the section is seldom circular and is thus not easily measurable. As in the case of yarns and fibers, fineness is usually specified by the relation of mass (weight) to length:

tex = \frac {mass (g)}{length (km)}   or   dtex = \frac {mass (dg)}{km}

Whereas for man-made fibers dtex is used almost exclusively, the Micronaire value is used worldwide for cotton.

The fineness scale is as follows:

Mic VALUE
FINENESS
up to 3.1
very fine
3.1-3.9
fine
4.0-4.9
medium (premium range)
5.0-5.9
slightly coarse
above 6
coarse

Conversion factor: dtex = Mic × 0.394 (heavily dependent on degree of maturity).

It should be remembered, however, that the Micronaire value does not always represent the actual fi neness of the fibers. Owing to the use of the air-throughflow method for measuring the Mi value, for example, a low average value is obtained where there is a high proportion of immature fibers, and this does not correspond to the true value for the spinnable fibers.

Specification by linear density (tex) is more accurate in such a case, but far harder to obtain. There is a further difficulty. Cotton is a natural fiber. It grows in various soils, in various climates, and with annually changing cultivation conditions. The fibers therefore cannot be homogeneous in their characteristics, including their fineness. Schenek  [1] indicates that the Mic value varied, in an extreme example, between 2.4 and 3.9 from bale to bale in a lot of 500 bales. Long-staple cotton varieties are commonly finer than medium-staple.