Wool is a natural fiber, an animal-derived textile that has been used by humans for thousands of years. Its classification is based on the fundamental difference between fibers that are harvested and those that are chemically created. Understanding this distinction, along with the unique chemical makeup of wool, clarifies why it is not considered synthetic.
Defining Natural and Synthetic Fibers
The textile industry classifies fibers based on their source and the extent of human-made chemical alteration required for their production. Natural fibers are obtained directly from a plant, animal, or geological source, requiring only mechanical processes like cleaning, spinning, and weaving. Examples include plant-based fibers like cotton and linen, or animal-based fibers such as silk and wool.
Synthetic fibers, in contrast, are entirely manufactured through complex chemical synthesis, most often using petrochemicals as their primary raw material. These fibers are essentially plastic polymers created in a factory and extruded into threads. Common synthetic materials include polyester, nylon, and acrylic, which are built from small molecular units joined together in a process called polymerization.
A third category is semi-synthetic or artificial fibers, which start with a natural material like wood pulp but undergo extensive chemical processing. Fibers like rayon and viscose fall into this group because their final structure is chemically regenerated from a natural cellulose base.
The Biological Origin of Wool
Wool is an animal fiber, obtained primarily from the fleece of domesticated sheep. Other animals yield specialized wool-like fibers, including cashmere and mohair from goats, angora from rabbits, and fibers from camelids like alpacas and llamas. The raw material is simply shorn from the animal, making it a renewable resource that regrows annually.
Wool’s composition is almost entirely keratin, a complex structural protein also found in human hair and skin. This protein structure is chemically distinct from plant fibers, which are mainly cellulose, and synthetic fibers, which are typically petroleum-based polymers. Keratin is formed by a complex arrangement of amino acids that create long polymer chains, giving the fiber its unique strength and flexibility.
Distinguishing Wool from Synthetic Counterparts
Wool’s protein structure grants it several properties that sharply contrast with synthetic imitators like acrylic and polyester. The natural crimp and complex architecture of wool fibers trap air, allowing the textile to regulate temperature by insulating in the cold and providing breathability in the heat. Wool also has a remarkable ability to absorb large amounts of moisture vapor—up to 30% of its weight—without feeling damp, a property known as moisture-wicking.
Synthetic fibers are designed for durability and low cost but often lack this natural performance. Materials like polyester and acrylic are non-porous and tend to trap heat and moisture against the skin, which can lead to odor retention. Furthermore, synthetic textiles shed microplastics when washed and persist in landfills for centuries.
As a natural protein, wool is inherently biodegradable, often breaking down in soil within a few months. Wool’s composition means it does not require the added chemical finishes, flame retardants, or plasticizers often applied to synthetic alternatives.