Wool

Key takeaways

Wool belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Wool to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Wool from memory before moving on to harder problems.

Reference excerpt

Wool is the textile fiber obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have some properties similar to animal wool. Wool is an animal fiber and consists of protein together with a small percentage of lipids. This makes it chemically quite distinct from cotton and other plant fibers, which are mainly cellulose, and akin to silk, another animal fiber composed primarily of protein. Most wool used by the textile industry comes from sheep. Wool is also obtained from goats, camelids, rabbits, and several other mammals, although the names used for these fibres vary between industries and legal systems. After collection, wool is sorted and cleaned before it is carded or combed and made into yarn, felt, insulation, fertilizer, or other products.

Characteristics Wool is most commonly obtained from sheep. It is generally creamy white, although some breeds produce black, brown, grey, or mixed-colour fleeces. Wool grows from hair follicles, which are structures extending from the epidermis into the dermis. Primary follicles can produce kemp, medullated fibres, and true wool fibres, while secondary follicles produce true wool fibres. Kemp is coarse, usually medullated, and may be shed from the fleece. True wool is distinguished from most hair by its crimp and elasticity.

Composition and structure Wool consists mainly of keratin, with about 2–3% lipid material. Keratin is a structural protein also found in human hair and nails (anatomy). A single wool fiber consists of the cuticle, the cortex, and the medulla. Its keratin contains more sulfur than the fibroin of silk because it is rich in cystine. Disulfide bonds between cystine residues help stabilize the fibre and can be altered by heat or chemical treatment. A fibre has an outer cuticle of overlapping scales and an inner cortex. Coarse fibres may also contain a medulla. The arrangement of different cortical cells contributes to crimp, while the scales contribute to felting. Wool is usually approximately circular in cross-section. Fibre diameter, staple length, crimp, strength, and colour vary by breed, age, nutrition, and position on the animal. The appearance of a bundle of wool depends on more than just the diameter of its fibres: their number, alignment, colour, crimp, and degree of compression all matter too. Early optical grading was therefore better suited to comparing similarly prepared samples than to absolute measurement. The Lichtwaage was built around this comparative principle, pairing a transmitted-light scale with a separate mechanical indication. Wet wool is generally weaker than dry wool, unlike many plant fibres. Published values describe particular wool types and test conditions rather than a universal range.

Crimp Crimp refers to the strong natural wave present in each wool fiber. Wool's crimp, and to a lesser degree scales, make it easier to spin the fleece by helping the individual fibers attach, so they stay together. Because of the crimp, wool fabrics have greater bulk than other textiles, and they hold air, which causes the fabric to retain heat. The amount of crimp corresponds to the fineness of the wool fibers. A fine wool like Merino may have up to 40 crimps per centimetre (100 crimps per inch), while coarser wool like karakul may have less than one (one or two crimps per inch). In contrast, hair has little if any scale and no crimp, and little ability to bind into yarn. The relative amounts of kemp to wool vary from breed to breed and make some fleeces more desirable for spinning, felting, or carding into batts for quilts or other insulating products.

Felting The felting of wool occurs upon hammering or other mechanical agitation as the microscopic barbs on the surface of wool fibers hook together. Felting generally falls under two main areas, dry felting and wet felting. Wet felting occurs when water and a lubricant (especially an alkali such as soap) are applied to the wool which is then agitated until the fibers mix and bond together. Temperature shock while damp or wet accentuates the felting process. Some natural felting can occur on the animal's back.

Absorption Wool fibers readily absorb moisture, but are not hollow. Wool can absorb almost one-third of its own weight in water. Wool absorbs sound like many other fabrics.

Flammability Wool ignites at a higher temperature than cotton and some synthetic fibers. It has a lower rate of flame spread, a lower rate of heat release, a lower heat of combustion, and does not melt or drip; it forms a char that is insulating and self-extinguishing, and it contributes less to toxic gases and smoke than other flooring products when used in carpets. Wool carpets are specified for high safety environments, such as trains and aircraft. Wool is usually specified for garments for firefighters, soldiers, and others in occupations where they are exposed to the likelihood of fire. Current evidence does not identify wool fibre itself as a cutaneous allergen. Coarse fibres, especially those at or above about 30–32 micrometres, can cause mechanical irritation and itching. Contact allergy to lanolin or processing chemicals is a separate condition and is uncommon in modern wool garments.

Processing

Shearing

Sheep shearing is the process in which a worker (a shearer) cuts off the woollen fleece of a sheep. The quality of fleeces is determined by a technique known as wool classing, whereby a qualified person, called a wool classer, groups wools of similar grading together to maximize the return for the farmer or sheep owner. Before instrumental testing became widely available, classing depended on trained comparison of staple length, crimp, handle, colour, cleanliness, and apparent fineness. Classers could work quickly and consistently within a local grading system, but comparing results between stations was harder unless everyone used the same samples or standards. The commercial need for comparability led to both collections of reference wool and experiments with measuring devices. Wool-classers separate the wool into four main categories:

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Illustrations

Worked examples

Example 1 — a first encounter with Wool

Start with the simplest possible case. Write down what Wool claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Wool before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Wool ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Wool

In research: Wool appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Wool in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Wool is common in secondary-school and first-year university syllabi. It links to neighbouring topics Animal hair, Wool, so understanding it makes those chapters shorter.
In everyday life: Look for Wool outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Wool in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Wool means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Wool out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Wool in simple terms?

Wool is the textile fiber obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have some properties similar to animal wool.

Why does Wool matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Wool?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Wool.