Wool is a long, slender, solid cylinder, crimped in shape. Its fiber structure consists of three layers: the scale layer, the cortex, and the medulla.
The scale layer: This is the outermost layer of wool. Its growth follows a specific direction, from the hair root to the hair tip. Each scale connects to the cortex at one end of the hair root, while the other end extends outwards, overlapping and overlapping. The density of scale coverage varies considerably depending on the wool breed. Finer wool has more scales, longer overlapping sections, and the scales are often ring-shaped. Coarser wool has fewer scales, shorter overlapping sections, and the scales are often corrugated or fish-scale-like, overlapping each other. Because the scale layer extends outwards and protrudes, increased friction between fibers creates felting, which strengthens the cohesion under humid and hot conditions. The scale layer also gives wool a good luster. The tough scale structure gives wool resistance to abrasion and staining.
Cortex: The cortex is the main component of wool fibers, composed of many protein cells called keratin or keratin. The cells are bonded together, with gaps between them. The cortex is the primary layer determining the physical, mechanical, and chemical properties of wool fibers. It is divided into two types: the orthocortex and the paracortex. In crimped wool fibers, under stress, they can be stretched to about 20% and return to their original crimped state after relaxation. The cells on the outer side of the crimp are called orthocortical cells, and those on the inner side are called paracortical cells. The orthocortex has a lower sulfur content than the paracortex, making it chemically more reactive and easier to dye. The paracortex, on the other hand, is the opposite. In high-quality fine wool, the two types of cortical cells are clustered on opposite sides of the wool shaft and intertwined along the fiber axis, a phenomenon known as bilateral isomerism.
Medulla: The medulla is located in the central part of the wool fiber and is an opaque, loose substance. Generally, fine wool lacks a medulla, while coarser wool has varying degrees of medulla. The more medulla a wool contains, the straighter and coarser it appears, and the lower its quality. Wool containing a large amount of medulla is brittle and easily broken, with less crimp, and the shriveled wool is called dead wool. Some wools have discontinuous medulla, with fine and coarse hairs on a single fiber; such wool is called two-type wool.
