Because I am not an expert on any of this, I will refer the reader to other sources of information, dedicating this segment to basic known issues. The fleece is composed of individual fibers. Each fiber has three concentric layers. The most superficial layer is called the cuticle, the next one is called the cortex and the inner layer is the medulla.

Cuticle: The cuticle is a layer of flat cells that serves as protection from the elements, like our skin. This layer is composed of scales, with one border under the next scale and all oriented the same way, similar to the scales of a fish. The exposed borders of these scales are serrated and uneven on the huacaya fiber with a diameter of 30 or more microns. The same is true for the suri fiber. The narrower diameter fiber has smoother scale contour. Because the borders do not jut out from the shaft, the fiber is more resistant to stains and very soft, but still takes dyes easily. The fineness and the smoothness of the fiber make the processing different from the processing of other natural fibers; therefore, machines have to be adjusted for these differences.

Cortex: In the huacaya, the cortex has two parts, the orthocortex and the paracortex; which run longitudinally on the fiber. These two structures are responsible for the crimp of the fiber, with the orthocortex always placed on the outside surface of the crimp. The suri fiber, which does not have crimp, does not have this differentiation. The cortex is made of fibrils (very narrow, long cells) that run along the fiber. The finer the fiber, the more percentage of cortex is present, and because of this, we believe that crimp is positively related to fineness.

Medulla: The medulla is the inner section of the fiber. It runs longitudinally inside the fiber and is hollow. The medulla appears fragmented in the longitudinal plane in fiber diameters between 20 and 30 microns. It is interrupted in fiber with diameters around 30 microns. It is continuous in fibers with diameters of 40 microns and very wide in those with diameters greater than 60 microns. It is nonexistent in diameters of less than 20 microns.

With the naked eye, the medullated fibers look like stiff hairs sticking up from the even surface of the fleece. They are also called “guard hairs”, and are more noticeable on the apron (front of the chest), under the belly, and on the legs. Because they are stiff, they detract from the softness and act differently from the finer fibers. They do not take dye well and must be removed during the fiber processing. They are measured as fibers over 30 microns in the histogram.