A wool staple is a naturally formed cluster or lock of wool fibres and not a single fibre. Very many staples together form a fleece.
The cluster of wool fibres is made by a cluster of follicles. The natural cluster of wool is held together because individual fibres have the ability to attach to each other so that they stay together. When removed from the sheep the underside of the fleece shows all its distinct individual staples.
For other textiles, the staple, having evolved from its usage with wool, is a measure of the quality of the fibre with regard to its length or fineness.
Staple strength is calculated as the force required to break per unit staple thickness, expressed as newtons per kilotex or N/tex. Position of Break (POB) is measured in conjunction with staple strength and is a measure of the position in the staple (base, mid or tip) where it will break given enough force.
The staple strength of wool is one of the major determining factors when spinning yarn as well as the sale price of greasy wool.
At least 40 staples must be measured to in order to conform to the Australian Standard. Wools under 30 newtons per kilotex are considered tender. Currently wools over 40 newtons per kilotex are preferred and attract a premium. Seasonal conditions or the health of the sheep may influence the soundness (strength) of the wool.
The staple length of the wool is the length of the staple, and highly correlated with mean fibre length in the top (hauteur).
Staple length generally determines the end use of wool, that is, whether it will be used in weaving or knitting. The longer wools, generally around 51 mm and longer and called combing types, are processed to worsted yarn. Short-stapled wools are more profitably used in the woollen section where high-grade material may be produced from superfine wool.
The Australian Standard requires that a sale lot has a minimum of 55 staples measured with the average calculated and produced. The variability of this measure is reported as the coefficient of variation (CV%).
Although traditionally staple length only referred to animal fibres, it is now also used when referring to manufactured fibres.
- "staple, n.3". OED Online. June 2011. Oxford University Press