Wool is a natural fiber that grows on sheep, made almost entirely of a protein called keratin: about 97% protein and 2 to 3% lipids, according to The Woolmark Company. Each fiber has a scaly outer layer and a spring-like core, and that structure is why wool can take up about 30% of its own weight in water without feeling wet, stretch and recover, and resist flame. Down-Under Wool has worked with Australian Merino wool and sheepskin since 1988, and this guide explains what wool is, what it is made of, where it comes from and what makes it different from other fibers.
What is wool?
Wool is the fiber that forms the fleece of a sheep. Sheep grow a new fleece every year, and it is shorn off, cleaned and spun into yarn for clothing, blankets, bedding and carpets. In everyday use, "wool" means sheep's wool; the soft coats of some other animals are also called wool, such as cashmere from goats and alpaca from alpacas, but they are usually sold under their own names.
Wool is a natural protein fiber, which sets it apart from plant fibers such as cotton and linen (made of cellulose) and from synthetic fibers such as polyester and acrylic (made from oil-based polymers). It is also different from sheepskin: wool is the shorn fiber, while sheepskin is the whole hide with the wool still attached. Our page on sheepskin vs wool compares the two side by side.
What is wool made of?
Wool is made of keratin, the same family of protein found in human hair and nails. The Woolmark Company puts the fiber at about 97% protein and 2 to 3% lipid (fatty) material, and its Merino guide notes small amounts of calcium, sodium and fat. Raw wool straight off the sheep also carries grease (lanolin), dried sweat, dust and plant matter, which are washed out before the wool is spun.
Under a microscope, each wool fiber has a layered structure:
| Part of the fiber | What it is | What it does |
|---|---|---|
| Cuticle | The outer shell: overlapping scales stacked like roof shingles, with a thin waxy coating | Sheds liquid water and stains, while tiny pores let water vapor pass into the fiber |
| Cortex | The bulk of the fiber: long, tapering keratin cells bundled together like a rope | Gives wool its strength, elasticity and natural crimp |
| Matrix | Sulfur-rich proteins packed around the keratin bundles | Attracts and holds moisture; linked to wool's flame resistance |
| Cell membrane complex | Proteins and waxy lipids that glue the cells together | Holds the fiber together; it is sensitive to strong alkali, so wool needs a gentle detergent |
Sources: Woolmark and the Science Learning Hub (University of Waikato).
The image above shows why wool behaves differently: the wool fibers on the left are covered in scales, while silk, linen, cotton and polyester are smooth or twisted.
Where does wool come from?
Wool comes from sheep, which are shorn, usually once a year. Shearing removes the fleece in one piece and, according to Woolmark, takes an experienced shearer between two and five minutes per sheep. The sheep then grows a new fleece, which is why wool is described as a renewable fiber.
Australia is the world's largest wool producer, growing about 345 million kilos a year, roughly a quarter of the world's wool, and its flock is overwhelmingly Merino (Woolmark). China, Russia, New Zealand, Argentina, South Africa, the UK and Uruguay are the other major producers. How wool got from the first domesticated sheep to modern mills, and how it is turned from fleece into yarn, is covered in our guide to the history of wool, wool processing and types of wool.
Is wool a natural fiber?
Yes, wool is a natural fiber: it grows on a living animal and is not made from petroleum. Woolmark describes wool as 100% natural, renewable and biodegradable, and notes that 100% Merino wool breaks down in both soil and seawater, so it does not add to microplastic pollution. We cover the sheepskin side of that story in are sheepskins sustainable and eco-friendly? Wool is also the most recycled apparel fiber, with up to 6% of all wool fiber mechanically recycled.
Wool is a natural protein fiber, like silk, alpaca and cashmere. Cotton and linen are natural cellulose (plant) fibers. That difference matters for care: protein fibers are damaged by bleach and harsh alkaline detergents, which is why we wash wool and sheepskin in a gentle wool wash such as Woolskin.
What makes wool special?
Wool's structure gives it a set of properties that no single synthetic fiber copies all at once:
| Property | Why it happens | What it means for you |
|---|---|---|
| Absorbs moisture | The sulfur-rich matrix attracts water molecules; wool can take up about 30% of its weight in water without feeling wet | Feels dry against the skin even when you sweat |
| Breathable | The fiber absorbs water vapor and releases it into the air while letting excess heat escape | Comfortable across a wide range of temperatures |
| Insulating | Natural crimp (waviness) traps still air between the fibers | Warm for its weight |
| Elastic and resilient | The spring-like keratin structure stretches and recovers | Resists wrinkles and keeps its shape |
| Resists odor | Keratin binds odor molecules until the wool is washed | Can be worn or slept on longer between washes |
| Flame resistant | Wool's chemistry makes it hard to ignite, and it does not melt or drip | Safer next to the skin than fibers that melt |
| Sheds liquid water | The waxy coating on the cuticle repels liquid | Resists light rain and staining (but is not waterproof) |
Sources: Woolmark, What is the wool fibre?; Science Learning Hub, wool fibre properties; Woolmark fact sheet, wool is resistant to fire.
Moisture absorption and breathability are the reasons fine wool is used next to the skin in bed. A dense Merino pile such as our Hospital Wool Fleece Bed Pad (1,050 grams of wool per square meter) or the Pressure Smart XD1900 Overlay (1,900 g/m²) puts those properties under a person who spends long hours lying down. Read more in is it good to sleep on wool?
Is wool hair or fur?
Wool is a type of animal hair, but it is not the same as human hair or fur. All three are made of keratin. What makes wool different is its crimp and its scales: wool fibers are wavy and covered in overlapping scales, which help them cling together in yarn and felt. Wool is also much finer than human hair. Woolmark puts human hair at about 50 to 100 microns across, while Merino wool is generally under 22 microns (a micron is one millionth of a meter).
Sheep are not usually described as having fur; their coat is called a fleece. When the hide is tanned with the fleece left on, it becomes sheepskin; see what sheepskin is and how it differs from lambskin.
Why does some wool feel itchy?
Wool feels itchy when its fibers are coarse, not because people are allergic to the wool fiber itself. A 2017 review in Acta Dermato-Venereologica (Zallmann et al.) found no evidence that wool fiber is an allergen; the prickle comes from coarse fibers, roughly 30 microns and thicker, whose stiff ends press into the skin. Fine Merino wool, under about 19.5 microns, is the wool used for next-to-skin garments. For the details, read our guide to merino wool allergy and whether merino is hypoallergenic.
What is wool used for?
Wool is used for clothing, bedding, home furnishings, insulation and health care. Which use a wool suits depends mostly on its fineness:
- Fine wool (mostly Merino) for soft knitwear, base layers, socks and bedding.
- Medium wool for woven suits, knitting yarns and furnishings.
- Broad (coarse) wool for carpets, rugs and upholstery, where strength matters more than softness.
- Health care: dense Merino wool pads and fleeces under people in bed or in a wheelchair, and loose combed wool to cushion toes and blisters, such as Footcare Lambswool, a rope of 23.5-micron Merino wool.
Around the house, wool turns up as underlays, duvets and pillow covers; browse our Merino wool bedding, or see why people choose a wool pillow.
Wool FAQs
Is wool a protein fiber?
Yes. Wool is a natural protein fiber made mainly of keratin, which is why it is grouped with silk, cashmere and alpaca rather than with plant fibers such as cotton.
Is wool made from sheep?
Yes, most wool is shorn from living sheep, which then grow a new fleece. Fibers from goats (cashmere, mohair), alpacas and Angora rabbits are also called wool in a broad sense, but they are usually sold under their own names.
Is wool a fabric?
Wool is a fiber first. It becomes a fabric when it is spun into yarn and then knitted, woven or felted. "Wool fabric" simply means cloth made from that yarn.
Is wool waterproof?
No, wool is water resistant rather than waterproof. The waxy coating on each fiber sheds light rain and spills, and the fiber can absorb about 30% of its weight in moisture before it feels wet, but heavy rain will soak through.
Is wool flammable?
Wool is naturally flame resistant. It is harder to ignite than cotton or synthetics and, unlike polyester and nylon, it does not melt or drip onto the skin. It can still burn in a sustained flame.
Does wool shrink?
Wool can shrink and felt when it is agitated in hot water, because its scales lock together. Washing it on a wool or gentle cycle in cool water with a mild wool wash prevents this; follow the care label.
Why is wool so warm?
Wool is warm because its crimped fibers trap still air, and air is a good insulator. It also absorbs water vapor from your skin, so you stay dry, and dry skin feels warmer.
Is wool better than cotton?
For warmth and moisture handling, usually yes. Wool absorbs moisture vapor and still feels dry, traps warm air and resists odor. Cotton is cheaper and easy to wash, but it feels wet and clammy once it is damp.
The short version
Wool is a natural, renewable protein fiber shorn from sheep. It is made of keratin, about 97% protein, with a scaly outer cuticle and a spring-like inner cortex. That structure lets wool absorb moisture and still feel dry, insulate, stretch and recover, resist odor and resist flame. Fine Merino wool is soft enough to wear or sleep on; coarse wool goes into carpets and rugs. To see what we make from Australian Merino wool, visit our wool bedding range, or contact us with any question; we have been answering them since 1988.
