We all know that wool has crimp and that fleeces from different breeds of sheep have different crimping patterns. Some breeds, such as Merino have a high number of crimps per inch of staple length while other breeds; such as Lincoln have only a few crimps per inch. But what, exactly is crimp, where does the crimp come from and why does it vary so much between breeds?

The American Heritage Dictionary defines crimp as “The natural curliness of wool fibers”. Mabel Ross, writing about wool crimp in her book, The Encyclopedia of Hand Spinning, tells us a bit more when she states: “The natural, regular wave present in most wool (but not hair or kemp) is called crimp”. The Sheepman’s Production Handbook by George E. Scott adds a bit more information defining crimp as: “The natural curl in the wool fiber, grown into the fiber from the follicle. Fibers vary widely in their crimp configuration. Crimp gives wool its natural resilience and elasticity”.

So we know that the fiber grows with a natural bend or crimp, and that crimp is responsible for the elasticity and resilience of wool. This occurs because the cortical cells of each wool fiber are composed of two types of cells called the ortho-cortex and the para-cortex. While these cells are made up of exactly the same material, namely keratin, and contain the same amino acids, they still differ slightly in composition. The difference between the two types of cells causes them to expand and contract at different rates as the different cells retain differing levels of moisture. Hence, the fiber crimps.

While there is only an approximation between the number of crimps per inch in a lock of wool and the fineness or diameter of the fibers of a particular fleece, the slower growing fleeces tend to be finer and have the most, best-defined number of crimps per inch of staple length. Breeds with faster rates of fleece growth will have fewer crimps per inch of staple length with the locks appearing to have a broad wavy pattern.

To count crimps per inch, care must be taken not to stretch the staple or the count will be wrong. To count crimps per inch (cpi), take a thin lock, lay it on a background that is of a contrasting color and count the bumps along one side of the lock.

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Another way to count crimp which works well with highly crimped fleeces is to take a piece of cardstock of a contrasting color and cut a little half inch long “window” into the cardstock. Lay the cardstock over the lock and then count the bumps and multiply by 2 to get the number of crimps per inch.