The relative importance of fibre properties in spinning has been well established:

• Diameter (D) is overwhelmingly the most important property
  
  
• The mean fibre length (H) is next in importance with an extra 10mm of length being able to compensate, approximately, for a 1μm increase in mean diameter for yarn strength and spinning performance although the yarn will still be less even.
  
  
• Fibre strength (bundle tenacity) is usually only of importance when the fibres have been damaged, for example by dyeing. There is relatively little variation in the strength of ecru (undyed and untreated) tops of Australian wool.
  
  
• Variation in diameter (CV_D) is normally of limited importance with 5 units of CV_D being able to be traded-off against 1μm. A top of 20μm and CV_D = 25% can be replaced by a top of 21μm and CV_D = 20% with no observable difference in yarn properties, spinning performance, fabric stiffness or next-to-skin comfort.
  
  
• Fibre curvature has little importance. It is not a stable property and if the wool has not been chemically treated most of the crimp present in the greasy wool can be recovered by relaxation of the top in warm water. High curvature wools tend to give slightly less even yarns and the yarns and fabrics contract more when wet relaxed.
  
  
• Variation in length (CV_H) has little effect on processing when other properties are well-matched. However, it is strongly correlated with H and with short-fibre content and extreme values are correlated with CV_D. The current evidence is that a wider range of lengths is slightly beneficial for yarn evenness but, provided the quality of combing has been good and there are no over-long (>200mm) fibres, then CV_H can be ignored.
  
  

Other characteristics of top properties that can be of importance include:

• Contaminants and faults. These include vegetable matter (VM), neps, slubs, coloured fibre and plastics. Tops from pure Australian wool have an excellent reputation for low contaminant levels and it is possible for the topmaker to select wools low in dark-fibre content.
  
  
• Lubricants/antistats and residuals. The total fatty matter (TFM) present in a top is a combination of what was left on the wool after scouring and what oils were added in topmaking. Therefore, it is difficult to determine the quality of scouring from a measure of TFM (solvent soluble residuals). There are other test methods for residuals (scourable solids and water soluble) but most spinners rely on the topmaker to scour correctly and add less than 1% of a suitable lubricant/antistat.
  
  

For weaving yarns, which need to be stronger and more abrasion resistant, it is normal to require H > 68 or 70mm with some premium tops of H > 80mm being available, while for knitting yarns which tend to have more fibres H > 55mm may be all that is specified. Settings in re-combing and drawing should be adjusted to suit the fibre length but it is usually not necessary to alter settings on the spinning frame as a function of H. There are some recent developments in spinning such as weavable singles (Sirospun and Solospun) and Compact/Condensed spinning which reduce yarn hairiness. There is also a small amount of air-jet, vortex, friction and OE spinning of wool. The relative importance of fibre properties is similar except that there may be different restrictions on fibre length.