Have you ever wondered why different fibers have different characteristics? Every fiber has its own unique physical properties that affect how they behave. Fiber testing is done for many reasons and there are different machines used for the job. They all measure the same characteristics: mean fiber diameter (MFD), standard deviation (SD), coefficient of variation (CV) and fiber over 30 microns (%>30). Newer machines also measure spin fineness (SF), comfort factor (CF), mean curvature (curv) and standard deviation of curvature (SDcurv).
MFD is the simplest parameter to define. It's the average of how thick or thin the fibers are and is casually discussed as fineness. Both the SD and CV are parameters of uniformity..how similar or dissimilar are the fibers in the sample? SD refers to the distribution of individual measurements around the mean, with a low SD indicating a high degree of uniformity. While SD is useful when comparing the uniformity of fleeces with a similar MFD, the CV of fiber diameter is more useful when comparing the uniformity of fleeces with different MFDs.
The CV is a percentage derived by dividing the SD by the MFD. The final quality that indicates uniformity is the percentage of fibers over 30 microns, sometimes called either the comfort factor or prickle factor, since coarser fibers are more irritating to the skin. These coarse fibers also tend to be straighter and their larger size causes them to drift to the outside of the yarn when spun where they can irritate the skin.
The mean curvature (MC) is another important parameter. It measure the average degree and amount of crimp present in the fiber. The MC is critical at all stages of textile manufacturing. High curvature fibers like merino wool are easier to process and spin into yarns with great elasticity and loft. Both the high MC and degree of uniformity (low SD, low CV and extremely low %>30) combine to make merino wool the fiber of choice for textile mills globally.
Additional fiber qualities that are of great importance to textile mills are staple length (SL), staple strength (SS) and position of break (POB). Genetics contributes highly to staple length, though environmental factors such as age, sex and reproductive status also influence SL. Nutrition and management are major contributors to both SS and POB. It's possible to tell when a young sheep was weaned since the fiber tends to be weaker at this point, even with the most kind and ethical management.
One fascinating physical characteristic that plays a role in fiber performance is scale structure. All protein fibers have scales on them, and it's the height, shape and structure of these scales that contribute to how the fiber itself performs. Fine wool like Rambouillet has many small scales packed tightly together with almost fish like scale shape. Genetics influence all of these characteristics and breeders work hard to produce wool with scale structures that will be extremely comfortable. Cashmere has jagged scales almost like broken glass, which can be irritating to some people's skin even though cashmere has a low MFD. Angora's scale structure is fascinating, since it almost looks like wave washed sand.
By now you’re probably wondering, why does this matter? These are the foundations of how fibers will perform and behave, and hopefully this helps you choose what fiber to use for a particular project. Fine fibers are great next to the skin, but a rug made out of 18 micron merino won’t last long. That’s a job better suited for a higher MFD wool. However, both wool for a sweater and wool for a rug needs to be uniform since uniform fiber is easier to process and performs better in the long run. Every single sheep breed was created through selective breeding for a particular use and to fulfill a specific need.
Curvature influences how fiber will behave in processing and in final use. High curvature fibers are more elastic and will process more easily. They’ll also help grab onto other fibers. Take our Rambouillet/Angora blend as an example. Rambouillet is a fine wool with a very high degree of curvature. Angora is just as fine if not finer, but it has almost no curvature. The Rambouillet’s curvature helps grab and hold onto the Angora. The two fibers have a very similar staple length, since we’re fortunate to have an extremely high quality source of Angora that’s unusually uniform for Angora. This similarity in staple length and high degree of uniformity mean a yarn produced from this blend should wear well, depending on how its spun and plied.
Scale affects how fiber feels. While Gotland is a fairly high MFD fiber, it’s deceptively soft because it’s extremely uniform and has a low scale height and long scale structure that’s similar to mohair in many ways. The uniformity of micron and scale structure makes Gotland deceptively soft.
This just scratches the surface. In our next newsletter, we'll take the leap into shearing and classing wool!
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