What Is Wool?

How is wool made?

Wool is made by shearing the fleece from living sheep, cleaning it, and spinning the fibres into yarn that is woven, knitted or felted into cloth. Sheep grow a new fleece every year, which is shorn seasonally, according to The Woolmark Company, the wool industry body.

• Cleaning: washing the raw fleece removes “wool grease”, the fatty substance that is purified to make lanolin (Britannica).
• Woollen spinning: usually uses shorter fibres and gives yarns that are thick and full (Britannica).
• Worsted spinning: usually uses longer fibres and gives yarns that are fine, smooth, firm and durable (Britannica).

Those yarns become cloths with their own names, among them flannel, gabardine, broadcloth, bouclé and Harris Tweed. Matted without spinning, wool fibres also make felt.

Where wool comes from

Wool use is prehistoric: Britannica describes people who clothed themselves in sheepskins and eventually learned to make yarn and fabric from the fibre.

What are the properties of wool?

Wool is warm, absorbent, resilient and easy to dye, but it shrinks and mats if it is agitated while wet.

• Composition: the fibre is chiefly the protein keratin (Britannica); Woolmark puts it at about 97% protein and 2–3% lipid material.
• Moisture: Britannica says wool can retain as much as 16 to 18 per cent of its weight in moisture, and that it becomes warmer to the wearer as it absorbs moisture from the air. Woolmark describes the fibre as hygroscopic: it holds moisture vapour without feeling wet.
• Crimp: fine wool fibres are wavy, with up to 30 waves per inch (12 per centimetre), according to Britannica. Woolmark says this crimp helps trap still air between skin and fabric.
• Resilience: the fibre returns to its original length after limited stretching or compression (Britannica).
• Felting shrinkage: wet fibres subjected to mechanical action become matted into packed masses (Britannica).
• Dye: wool has good to excellent affinity for dyestuffs (Britannica).
• Weak points: strong alkalis and high temperatures damage it (Britannica).

How is wool graded or measured?

Wool is measured mainly by fibre diameter, in microns (one millionth of a metre), and by fibre length; finer fibres feel softer against the skin. Woolmark explains that fine Merino fibres bend easily, which reduces the prickle associated with coarser wool.

Under US rules, cashmere must average 19 microns or less, so a fine Merino can overlap with it in diameter.

How does wool appear on a clothing label?

On a label, wool appears as “wool” with its percentage by weight (and, in the US, as “recycled wool” when it has been reclaimed), but the US and the EU do not define the word the same way.

Under US rules

• The FTC’s guide to the Wool Act says “wool” may be used for the fleece of the sheep or lamb and for the hair of the Angora goat, Cashmere goat, camel, alpaca, llama and vicuña. A seller may use the specialty name instead, such as mohair or cashmere, but must then state its percentage.
• Fibres under 5% are normally listed as “other fiber” unless they have a clearly established functional significance, but the percentage of wool or recycled wool “shall always be stated” (16 CFR 300.3(b)).
• Recycled wool is wool returned to a fibrous state after being woven, knitted or felted into a wool product, and it must be named as recycled wool (FTC).
• “Virgin” or “new” may describe wool only when none of it has been reclaimed from a previously manufactured or used product (16 CFR 300.20).
• The label must also give the country where the product was processed or manufactured, and the name or registered identification number (RN) of the manufacturer or another responsible business (16 CFR 300.3(a)).

Under EU rules

• Annex I of Regulation (EU) No 1007/2011 reserves “wool” for fibre from sheep’s or lambs’ fleeces, or a mixture of that with listed animal hairs such as alpaca, camel, cashmere, mohair and vicuña. Those hairs take their own names, which may be followed by “wool” or “hair”.
• A “100%”, “pure” or “all” label may still contain up to 2% extraneous fibres, or 5% for carded products, where technically unavoidable (Article 7).
• “Fleece wool” or “virgin wool” is allowed only for a product made exclusively of wool that has never been incorporated in a finished product, has not been spun or felted beyond what making that product requires, and has not been damaged by treatment or use; extraneous fibres may not exceed 0.3% (Article 8).
• In a blend, “virgin wool” is allowed only if all the wool meets that test and makes up at least 25% of the weight, and the full percentage composition is given; a scribbled mixture may contain only one other fibre (Article 8(2)).
• The Regulation has no separate “recycled wool” fibre name; wool reclaimed from a finished product cannot be called fleece wool or virgin wool.

How do you tell good wool from poor wool?

Good wool shows on the label first, with a clear fibre percentage and any recycled or virgin status, and then in the hand: it feels smooth rather than prickly and springs back when crushed. Check:

1. Read the fibre line. On a US label, wool is always declared with its percentage, so the line shows how much wool a “wool blend” holds. If the line lists only acrylic or polyester, there is no declared wool. The same applies to fleece fabric: check its fibre line.
2. Treat “Merino” as a breed, not a grade. Neither the FTC’s list of wool fibres nor EU Annex I uses the word. Woolmark’s Merino range runs up to about 22–24 microns, so if softness is the point, ask the maker for the micron figure; below about 19.5 is the range Woolmark says suits next-to-skin wear.
3. Do the wrist test. Rub the fabric on the inside of your wrist. Prickle points to coarser fibres; fine fibres bend away from the skin.
4. Crush a corner. Squeeze it in your fist for a few seconds and let go. Wool’s resilience should let it recover.
5. Look at the yarn. Fine, smooth, firm yarn suggests worsted spinning; thick, full yarn suggests woollen.

Red flags: “wool” in a product name with no wool percentage in the fibre line; and “Merino” or “superfine” offered as proof of softness with no micron figure.

How do you care for wool?

Follow the care label first; otherwise wash wool gently in cool water with a mild detergent and as little agitation as possible, then dry it flat, because wet fibres mat together under mechanical action (felting shrinkage).

• Washing: Britannica advises mild reagents at temperatures below 20 °C, with minimum mechanical action. Woolmark recommends a neutral, mild wool detergent and turning garments inside out.
• Drying: dry a jumper flat unless its care label allows tumble drying, at room temperature away from direct sunlight or heat (Woolmark).
• Pressing: use steam and the wool setting, and avoid ironing the fabric when it is completely dry (Woolmark).
• Storage: store garments clean, in airtight bags or containers, with any moth repellent kept off the fabric. Hang woven wool on shaped or padded hangers and fold knits into drawers (Woolmark).

Is wool sustainable?

Wool is renewable and, according to the wool industry, biodegradable, but sheep farming carries animal-welfare and climate costs, so the answer depends on how a particular wool was produced.

• Renewable: sheep grow a new fleece each year (Woolmark).
• End of life: Woolmark states that 100% Merino wool biodegrades in land and marine environments, without giving a timeframe, and that up to 6% of all wool fibre is mechanically recycled. These are industry figures.
• Climate: sheep are ruminants and produce methane, a potent greenhouse gas, as part of digestion (Textile Exchange).
• Animal welfare: Textile Exchange names mishandling during shearing as a risk, and describes mulesing as the removal or destruction of wool-bearing skin.
• Certification: the Responsible Wool Standard is a voluntary global standard that addresses the welfare of sheep and the land they graze, with certification required at every stage of the supply chain (Textile Exchange).