Fineness of man-made fibres can be selected within a wide range and adapted to the intended application. Nowadays, distinctions are drawn in accordance with the following scale:

  • Super finest fibres below 0.1 dtex
  • Finest fibres (micro fibres) up to 1 dtex
  • Fine fibres up to 2.5 dtex
  • Medium-fine fibres up to 7 dtex
  • Coarse fibres up to 70 dtex
  • Coarsest fibres above 70 dtex.

The short-staple spinning mill processes almost exclusively fine fibres between about 0.8 and 3.3 dtex. Though there is an increase in using microfibres below 1 dtex they are still not commodity fibre products for the staple fibre spinning process.

Finest and superfine fibres are used for the manufacture of synthetic leather, for very fine velour and velvets where an extremely soft feel is required, for filters and lining materials, etc.

As was described in The Rieter Manual of Spinning – Volume 1 the fibre fineness is one of the most important fibre characteristics and it affects virtually every yarn property. All properties improve with increasing fineness because with finer fibres more individual fibres can be packed into a yarn of a given section.

The influence of fibre fineness on, for example, yarn strength, evenness and elongation is therefore very high and can be seen in Fig. 14 [4].

The number of thread breaks also declines with the use of fine fibres. Higher efficiency is then achieved in the weaving room. However, fine fibres are more expensive than coarse fibres, and finest fibres are notably more expensive. Furthermore, finer fibres always give rise to greater processing problems in the blowroom and the carding room. So the production rate has to be reduced significantly.

Fig. 14 – The influence of fibre fineness on yarn characteristics