What is sheep's wool structure?

Many of us love knitting sheep's wool, but do we really know what wool is? I'd like to shed a little light on the subject here, because wool is a complex (and fascinating!) fibre and there's a lot to be said for it.

As you may have already noticed, raw wool has a greasy appearance. This is actually a wax with a complex chemical composition, which is used to make lanolin. The fibres are also covered in wool grease, another complex chemical mixture that solubilises in water. It is therefore important to wash the wool thoroughly to remove the grease and wool grease. Wool will lose up to twice its weight after washing!

raw wool

Wool fibre is made up of pith at its centre, surrounded by a cortex. Did you know that most of this cortex is made up of keratin, like our hair? Finally, the surface of the fibre is made up of cuticles, resembling scales that can open and close depending on the climatic conditions (see figure below). This characteristic of wool is its strength, and I'll tell you more about it in a blog post dedicated to caring for your knitwear.

Schematic of the internal structure of the wool fibre (a) drawn by Bruce Fraser, Tom MacRae and colleagues, together with the TEM (transmission electron microscopy) image of the cross-section (b) and SEM image of the surface (c) of the wool fibre. surface (c), of the wool fibre. (Hassan and Carr, 2019, Journal of Advanced Research)

First of all, we need to distinguish wool, which has virtually no pith, from hair and jars, which have more pith. It's the latter that you don't want to find in knitting yarn, as these fibres are harder and therefore unpleasant to the touch! So it's important to sort the wool properly to remove the hair and the pith before considering turning it into yarn.

Secondly, wool fibres are classified according to their diameter. For example, the finest fibres have a diameter of less than 22 micrometres, and the coarsest have a diameter of more than 36 micrometres. But these values are only averages. In fact, the fineness of wool varies greatly from one breed of sheep to another, from one farm to another within the same breed and even within the same flock. This is particularly true of ewes of the lourdaise breed. Wool from the same flock is very heterogeneous, so it's essential to find the best fibres to use to produce the knitting yarn. This is what I strive to do to offer you quality Pyrenean wool yarns!

I hope this article has given you some answers about the structure of wool and don't hesitate to come back to me if you have any questions.

Fanny

Founder of Knitty and Woolly