Learn More About Wool

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Learn More About Wool

Wool is a fiber, or modified hair, that grows from the skin of sheep. Because it is formed as a living substance, its growth is regulated by the inherited characteristics of the sheep and by the general condition of the sheep producing it.

Wool is a versatile product in demand mainly because of its physical characteristics that directly influence wearer comfort, processing performance, durability, and textile attributes.

The use of wool as a textile fiber dates back to 4000 B.C. when it was used as such by the Babylonians. Its unique physical and chemical characteristics have been responsible for its great versatility and high value in the manufacture of clothing.

Sheep Wool Fiber

Wool is the fibrous covering from sheep and is by far the most important animal fiber used in textiles. It appears to have been the earliest fiber to be spun and woven into cloth. Wool belongs to a family of proteins, the keratins, that also includes hair and other types of animal protective tissues such as horn, nails, feathers, beaks, and outer skin layers. The relative importance of wool as a textile fiber has declined over the past decades with the increasing use of synthetic fibers for textile products.

The principal characteristics of clean wool types are an average diameter, measured in micrometers (referred to as microns), and average length, measured in millimeters. Essentially all fine diameter wool is produced by merino sheep or merino cross-breeds. Over 75% of the sheep in Australia (the world’s largest wool producer) are merino sheep, which are also bred in large numbers in South Africa, Argentina, and the former USSR. The softness, fineness, and lightness of fabrics are determined primarily by fiber diameter, and so the price is very sensitive to the mean diameter.

Raw wool from sheep contains other constituents considered contaminants by wool processors. These can vary in content according to breed, environment, and position of the wool on the sheep.

Shrinkage of Wool Textiles

Two mechanisms of fabric shrinkage are observed for wool; relaxation shrinkage and felting shrinkage. Relaxation shrinkage occurs when a fabric or yarn made from any textile fiber is first immersed in water. It results from the release of temporarily-set strains imparted during previous processing operations such as spinning, knitting, and fabric finishing. Relaxation shrinkage also occurs when a knitted garment or fabric is immersed in water after it has been dried while in a stretched state (for example by line drying).

Shrink-resist treatments are directed at preventing felting shrinkage, whereas minimization of relaxation shrinkage requires careful control during fabric finishing. Felting of loose fibers results in entanglement, whereas in fabrics fiber migration inside and between yarns reduces the fabric area, ie, shrinkage occurs.

The term shrink-resistant is preferred to shrink-proofed, although in recent years emphasis has switched to performance-related terms, such as hand-washable and machine-washable. A recent trend is to use the term easy-care, which for knitwear means resistance to felting shrinkage under severe conditions, including tumble drying. It also includes assessment of the fabric appearance after testing. For woven garments, this includes retention of pleats or creases as well as smooth drying performance.

Similar Animal Fibers

Alpaca: The Alpaca (Vicugna pacos) is a domesticated South American camelid species whose wild ancestor is the vicuña.

Llama: The llama (Lama glama) is the other domesticated South American camelid species, its wild ancestor being the guanaco.

Vicuña: The vicuña (Vicugna vicugna) is the smaller of the two wild South American camelids and its undercoat fibers are extremely valuable and “special”, not only for its textile characteristics but also for its rareness and association to exotic environments and culture.

Guanaco: The guanaco (Lama guanicoe) is the biggest of the two wild South American camelid species and its population is much larger than that of the Vicuña.

Mohair: Angora goats from northwest of Argentina’s Patagonia produce mohair of competitive quality.