Wool is a very versatile product, used to make carpets, blankets, clothing, and many other materials. Wool is a good insulating material, can absorb water or allow for evaporation of water, is resistant to fire, and is very durable. Part of the reason why wool is so versatile is the unique properties it has, some of which relate to how wool is formed, some relate to the wool structure.
Wool structural characteristics
Some of the unique characteristics of wool relate to its structure. One of the structural characteristics of wool is crimp. Crimp is the waviness of the wool fiber. This waviness is caused by how the proteins that make up the fiber are arranged. This is the structural characteristic of wool that holds air, insulating against cold or heat.
Wool is made of 19 different amino acids, the building blocks of proteins. Like nails, horns, and hooves, wool has structural origins based on keratin. Skin follicles produce wool, much like the follicles in our skin produce hair. Wool fibers also have similar structures to hair. Each fiber has a thin outer layer, a cuticle, a cortex, and in some fibers, a medulla.
The thin outer layer is known as the epicuticle. This layer is very thin, approximately 1/100th of a micron (µ). The epicuticle is very hydrophobic, meaning it doesn’t like water. This is part of why wool is so good at repelling water.
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Wool is measured primarily based on fiber diameter. Since wool fibers are very narrow, the diameter is measured in microns. For reference, one micron is approximately 1/25,400th of an inch.
The cuticle is an overlapping series of protective flattened cells known as scales. Cuticle scales are about 0.5 to 1.0 micron thick. Cuticle scales overlap slightly, and the protruding edges point toward the tip of the fiber.
The cortex is one of the largest parts of the wool fiber and is where many of the unique properties of wool fiber. Cortex cells are longer than they are wide. These cells can be up to 115 microns long but only two to five microns wide.
The medulla, a central core is usually found in medium and coarse wools. Wool narrower in diameter than 28 microns usually doesn’t have a medulla. Medulla areas are thought to be brought about by incomplete filling of the fiber with keratin, resulting in a hollow or spongy core area.
Wool use is measured primarily based on fiber diameter and staple length. These two measurements determine what the wool will be used for and its value. Other factors that influence the end use of wool include strength of the wool, color, variability of staple or diameter, any felting (matting) that occurs, and contamination with vegetable matter or other foreign material.
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Note: This article originally was published in the Marquette County Tribune, Waushara Argus, and/or the Berlin Journal. This article was written by Lyssa Seefeldt, UW-Extension Agriculture Agent for Marquette County unless otherwise noted.