Wool

 

Wool is one of the world's oldest textile fibers. Wool is commonly used to describe fiber derived from sheep or lambs. Because its qualities are similar to sheep's wool, the hair of a few other animals can legally be called wool as well. The fiber from alpaca, camel, llama, vicua, Cashmere goat, and Angora goat can be labeled as wool by the US government, but they can also be labeled by their own fiber names.

Sheep were domesticated around 10,000 years ago in Central Asia to provide a ready source of meat, milk, and hides for clothing. Humans discovered that twisting thin strands of wool fiber together forms a continuous length of yarn as they worked with the hair from sheep hides. They eventually discovered that interlacing the yarn would form a fabric. Fabric became a second skin once yarn and fabric production became part of the human knowledge base. The earliest surviving fragments of wool cloth were discovered in Egypt between 4000 and 3400 B.C.E.

The first wild sheep had a two-layered coat. The coat closest to the body was a fine, downy wool undercoat. This was shielded by guard hair that was long, coarse, and straight. Because some sheep had higher-quality fiber than others, breeders chose sheep with more undercoat and less guard hair. In the early 2000s, the majority of sheep raised for wool production produced primarily undercoat fiber.

The cuticle, cortex, and medulla are the three layers of a wool fiber. The cuticle is the outer layer of overlapping scales that makes up approximately 10% of the fiber. The cortex, which makes up about 90% of the fiber, is made up of millions of long cells held together by a strong natural binding material. The cortex contains two types of cells that behave differently to give wool fiber its distinctive "crimp" or waviness when viewed from the side. When present, the medulla is a latticework of air-filled cells located in the middle of the cortex. A fiber with a large medulla is weak and difficult to dye.

Wool Production

Shearing

When humans first used wool fiber, they collected fiber shed by sheep during their spring molt. When humans domesticated sheep, they bred them to shed less wool so that it could be removed when it was convenient. The first step in wool production in the early twenty-first century is shearing the sheep's wool (cutting). Once off the animal, one sheep's fleece is bundled together, clean side in.

Teasing out the Meaning of Wool Fiber Terms

Grading and Sorting

Each fleece is examined, graded, and sorted individually. The fleece is graded for fiber fineness (diameter), length, crimp (a uniform waviness), color, kemp (thick hair fibers that dye poorly), strength, and elasticity after the tangled and dirty parts are removed. The diameter of the finest wool ranges between 10 and 20 microns (one micron equals 1/20,000 of an inch). Fine wool is luxurious and soft, similar to the fiber in a cotton ball. Coarse wool is stiff and bristly, making it ideal for carpet. Wool fiber ranges in length from 1 to 14 inches. Fine combing wools are 2.5 inches or longer in length, while coarse wools are 1.5 inches or less. While there are as many colors of sheep as there are of dogs and cats, white is the most common and has historically been the most valuable. Sorting separates the individual fleece into different qualities, with the shoulders and sides providing the highest quality and the legs providing the lowest.

Scouring

Wool must be cleaned of natural impurities before further processing. Impurities include lanolin, a greasy substance that oils the wool fiber and helps the sheep's coat shed water. Dirt, vegetable matter, and perspiration or suint are some other impurities (pronounced swint). The wool is scoured by washing it in a detergent solution that removes the oil and dirt. Grease wool is created when some lanolin is left on the wool fibers to provide water repellency.

Blending

Sorted fleeces of a specific quality are thoroughly mixed together to achieve the desired consistency of wool quality. Other fibers, such as spandex or nylon, may be added during this step to achieve an intimate blending of the fibers prior to spinning into yarn.

Stock Dyeing

Before spinning it into yarn, clean fiber can be dyed. This is known as stock dyeing. Dyed fiber can then be blended to create a yarn with a heather effect and multiple fiber colors.

Carding

To make an even yarn, the fibers must be separated, spread out evenly, and encouraged to lie relatively parallel with one another. The carding step creates a continuous strand of untwisted fibers, which is then drawn into a finer diameter strand before being twisted into yarn.

Woolen System

The woolen system of yarn production is used when a soft, fuzzy texture in fabric is desired. The fiber is carded several times during this process. This system can handle wool fibers of various lengths and types. Woolen cloth is cloth that is made from yarn spun on the woolen system. Tweeds, sweater knits, and flannel are common fabrics.

Combing (worsted)

The fiber must be combed in order to produce a smooth and uniformly textured fabric. Combing straightens and parallelizes the fibers. It removes short fibers as well as nearly all foreign matter from the fiber matrix. Carded yarns are coarser, dirtier, weaker, and less lustrous than combed yarns. Gabardine and serge are two worsted wool fabrics.

Spinning

Spinning is the final step in the yarn-making process. This draws out the fiber mass and thins it to the desired diameter before twisting the fibers into a yarn to stabilize the strand.

Yarn Dyeing

Yarn dyeing is the process of coloring wool in the yarn stage before it is woven or knitted into fabric. In weaving and knitting, dyed yarn creates plaids, checks, and other color effects.

Weaving

A woven fabric is created by interlacing two or more sets of yarns at right angles to one another. In the weaving process, both woolen and worsted yarns can be used. Fabrics made with woolen yarns are known as woolens, while those made with worsted yarns are known as worsteds.

Knitting

Knitted fabric is created by interlacing one or more yarns. Woolen or worsted yarns can be used in knitting, but woolen yarns are more commonly used. Garments can be knit into shape, or flat knitted fabric that must be cut and sewn into a garment can be created.

Piece Dyeing

After a fabric has been woven or knitted, pieces of it can be immersed in a dye bath to give it color. Piece dyeing produces a solid color fabric in most cases. Multiple color effects are possible when yarns of different fibers are combined in one fabric.

Finishing

A finished fabric requires additional treatment before it is suitable for consumer use. Wool fabrics can be finished in a variety of ways, including mending to repair weaving or knitting damage, wet finishes to control shrinkage and make the fabric more dense, napping to brush up a fuzzy surface, and singeing (burning) to eliminate long yarn ends. A final press is applied to wool fabric to smooth out wrinkles from previous finishing processes.

The Properties of Wool

Wool's natural qualities are the reason it has been used for thousands of years. Textile scientists have not completely replicated its superior properties. Wool is a natural masterpiece that serves as a standard against which other fibers are measured.

Resiliency and Elasticity

Wool fiber is pliable and elastic. It has the ability to bend 30,000 times without breaking or being damaged. The cortex cells, which naturally coil like springs to form crimp, are responsible for its natural elasticity. The elasticity makes it comfortable to wear because it conforms to the shape of the body and aids in the disappearance of wrinkles from wool garments when allowed to rest. Wool's tenacity is demonstrated when it stretches and returns to its original shape. Dry wool fiber can be stretched up to 30% without causing any damage. Wet wool can stretch up to 70%, but it is weaker, so washed wool must be handled with care. Wool's resilience allows it to last longer and keep its good appearance longer than many other fibers.

Comfort

Wool clothing is extremely comfortable in both hot and cold weather. Its intricate cellular structure allows it to absorb water vapor while repelling liquid. Wool absorbs the body's water vapor, leaving a dry layer of air next to the skin to trap body heat, keeping the body warm. The crimp in the wool fibers separates each fiber from the next, resulting in small pockets of air trapped between the fibers. This trapped air acts as an excellent insulator.

Wool is comfortable in hot weather because it absorbs perspiration vapor from the body, keeping the body cool. Perspiration evaporates, allowing the body to naturally cool. With its insulating barrier of air pockets, the crimp that helps keep the body warm in cold weather blocks out much of the outside heat. This assists the body in maintaining a constant temperature.

Wool's insulating properties protect against temperature changes and allow the body to breathe. Wool absorbs moisture but repels liquids. The scales on the outside of the fiber keep the liquid on the wool fabric's surface. If it rains, the raindrops will take some time to penetrate wool clothing, so wool keeps the wearer dry. When wool gets wet, it releases heat and keeps the wearer warm. Wool can absorb up to 30% of its own weight in moisture before becoming saturated.

Flame Resistance

Wool is naturally fire resistant due to its ability to absorb water vapor from the air. Wool will eventually burn, but it will not sustain a flame. When the flame source is removed, the wool self-extinguishes, leaving an ash that can be easily brushed away. Wool does not melt when heated, so it will not adhere to the skin.

Resistance to Static Electricity

Wool has a low tendency to accumulate static electricity due to its ability to absorb moisture from the air. Wool clothing is less likely to "sparkle" and cling to the body. Because static electricity does not attract dust from the air, wool resists dirt and stays cleaner longer than other materials. Furthermore, the wool's scales prevent dirt from penetrating the surface. Wool is easier to clean because of these same characteristics.

Felting

When wool fibers are subjected to a combination of heat, moisture, pressure, and agitation, they interlock and felt. The scales on the fiber are oriented in one direction, allowing it to move more easily in one direction than another. This is the effect of differential friction. Wool fiber's scales become locked together as it is moistened, rubbed, and warmed. Wool fiber can be felted directly into a fabric rather than first being spun into yarn. It also enables wool fabrics to be finished with "fulling," a controlled form of felting. "Fulling" increases the thickness and density of a fabric. Wool's ability to felt makes washing difficult because heat, moisture, and agitation will encourage felting and permanent shrinking.