Wool fiber has a natural crimp due to its unique chemical and physical structure. This causes the fiber to bend and turn, giving wool an inherent three-dimensional crimp. Because it is naturally elastic and resilient, wool imparts to all products that are made from it, many unique properties: rapid wrinkle recovery, durability, bulk, loft, warmth and resistance to abrasion.
Wool is a year-round fiber. Wool can easily absorb up to 30 percent of its weight in moisture without feeling damp or clammy. The ability of wool to absorb moisture makes it comfortable in both warm and cold conditions. By absorbing perspiration, wool enhances the body’s own cooling system and helps keep the skin dry. This characteristic makes wool a versatile all-season fabric.
Wool also keeps you warm in the winter by absorbing perspiration, allowing the body to generate heat faster than it is lost to the atmosphere.
Resistance to Flame
Because wool contains moisture in every fiber, it resists flame without chemical treatment. Instead of burning freely when touched by flame, wool chars and stops burning when it is removed from the source of the flame. Wool is self-extinguishing; it will not support combustion. This is why wool blankets are recommended for use in extinguishing small fires.
Wool absorbs many different dyes deeply, uniformly and directly without the use of other chemicals. Because of this ability, wool is known for the beautiful, rich colors that can be achieved.
The flexibility of the wool fiber also makes it more durable. A single wool fiber can be bent back on itself more than 20,000 times without breaking compared to 3,000 times for cotton and 2,000 times for silk. The natural elasticity of wool also makes wool fabrics resistant to tearing. In addition, the outer skin of the wool fiber acts as a protective film giving wool cloth improved resistance to abrasion.
Natural Felting Properties
The outer layer of wool is made up of small scales that contribute to wool’s property of felting. Agitation, friction and pressure along with heat and moisture cause the edges of wool fibers to interlock, preventing the fiber from returning to its original position. This shrinkage, which occurs, is irreversible.
The felting property of wool is both an advantage and a disadvantage. In a controlled situation, the felting process is called "fulling" or "milling" and creates a softer finish for woven wool fabrics. Felting is also crucial to the production of a wide variety of non-woven wool fabrics for hats and industrial uses.
Felting is considered a disadvantage because it makes washing untreated wool fabrics difficult. Treatments have been developed to prevent shrinkage due to felting. The machine wash label certifies that wool has been treated for machine washability and dryability. To produce a washable wool product, wool fibers are coated with a film to reduce end-to-end differential friction, thereby eliminating the entanglement that produces shrinkage.
Wool fibers can be stretched up to 50 percent of their original length when wet and 30 percent when dry. But when the tension is released, the wool fiber will bounce back to its original shape.
Because wool fibers are weaker when wet, a wool garment should not be hung to dry. Instead, it should be laid flat on a towel to dry to keep its original shape. Recovery from stress takes place faster when the fiber is in a humid environment, which is why steaming a wool garment will freshen the fabric and why a steam iron is recommended for pressing wool.
Resistance to Compression
Resistance to compression values are useful in assessing the suitability of wool for specific end uses. Resistance to compression (R to C) is the force per unit area required to compress a fixed mass of wool to a fixed volume. Resistance to compression is related to fiber diameter and the form and frequency of crimp.
For instance, low and medium R to C wools tend to be softer, more susceptible to felting, easier to process and produce strong fabrics. On the other hand, high R to C wools have a harsher handle, are resistant to felting and are bulkier.
Resistance to compression studies conducted by Texas A&M University prove American wool is well-suited to produce the finest of fabrics as well as wool batting for the production of futons and other bedding materials. These studies confirmed the fact that there are a good variety of low, medium and high resistant to compression wools available in the U.S. The majority of the wool finer than 28 micron in this test was analyzed as being in the middle resistant to compression range (53%). On the other hand, some 73 percent of the wool coarser than 28 micron was evaluated to be highly resistant to compression. See chart below:
Prepared by the American Sheep Industry Association, Inc.
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