A Practical Guide to Wool, Wool Blends, and Wool-Like Synthetics

Micron count is the number that shapes the feel

Wool is graded primarily by the average diameter of its fibres, measured in microns. The finer the fibre, the softer the fabric feels against skin and the less it prickles at the neck and wrist. The trade-off is that finer wool is less resistant to abrasion, so extra-fine wool blends are more common in shirts and next-to-skin garments than in outerwear or upholstery.

Reading a wool blend percentage honestly

Composition labels list fibres in descending order by weight. A tag reading 80% wool and 20% polyamide describes a common jumper blend, where the polyamide (nylon) is added to reinforce elbows and cuffs. The addition of even 10 to 15% synthetic fibre roughly doubles the abrasion life of an otherwise pure wool knit, at the cost of some breathability and thermal buffering.

Below about 50% wool the fabric loses much of the properties that wool is chosen for. A tag reading 30% wool and 70% acrylic behaves more like an acrylic garment with a hint of wool character. The lower the wool proportion, the more likely the piece will build static charge in dry indoor air and the less well it will regulate body temperature.

The Woolmark and related certifications

The Woolmark logo, administered by the Woolmark Company, indicates a garment that meets defined composition, strength, and colourfastness standards. The plain Woolmark denotes 100% new wool. Woolmark Blend indicates at least 50% new wool with tested performance. The mark does not guarantee luxury, but it does guarantee that the wool content, fibre type, and processing meet the published specification.

Care symbols worth knowing at a glance

• Wash tub with a hand symbol: hand wash only. Machine agitation causes wool fibres to interlock and shrink permanently.
• Wash tub with two lines beneath: very gentle machine cycle, sometimes labelled wool cycle on modern machines. Water temperature under 30°C.
• Circle with a P inside: dry clean using perchloroethylene solvent. Common on tailored wool garments.
• Triangle crossed out: no chlorine bleach. Chlorine attacks the disulphide bonds in wool keratin and yellows the fabric.
• Iron with dots: one dot for cool, two dots for warm, three dots for hot. Wool usually accepts one or two dots, with steam.

Failure signs that appear over time

1. Pilling at high friction points such as underarms and where a strap crosses the shoulder. Fine wool pills more readily than coarse wool, and blends with a small percentage of nylon pill less than pure wool.
2. Felt-like patches after an accidental warm wash. The fibres have interlocked irreversibly. The garment can no longer be relaxed back to its original dimensions.
3. A greasy sheen at cuffs and collar, from natural skin oils bonding with lanolin residues. Regular airing between wears reduces build-up.
4. Small holes appearing in stored garments, often the sign of clothes moth larvae feeding on the keratin. Cedar or lavender in storage acts as a mild repellent.
5. Loss of loft in a wool duvet or filling, indicating fibre breakage from repeated compression.

The Wikipedia entry on wool covers the microstructure that gives the fibre its properties. Related guides include cotton bedding thread count, bamboo fabric labels, and synthetic composition tags.

Wool-like synthetics on the composition tag

Several synthetic fibres are engineered to mimic the hand, warmth, or drape of wool. On a composition tag they appear under their own generic names. The visual similarity in a jumper is easy to notice; the behavioural differences take one wash to reveal.

Acrylic (polyacrylonitrile) contains at least 85% acrylonitrile monomer under ISO 2076. It was developed in the 1940s to imitate wool and remains the dominant wool substitute in mass-market knitwear. Its low moisture regain of around 1% is why acrylic jumpers feel warm indoors but cold and clammy in damp weather: the fibre does not absorb perspiration or ambient humidity into its structure. Wool at 15% regain buffers up to three times its weight in moisture before feeling wet on the skin.

Modacrylic contains 35% to 85% acrylonitrile, with the remainder made up of vinyl chloride or vinylidene chloride. That chlorine content gives modacrylic inherent flame resistance and a limiting oxygen index above 26%, compared with 18% for wool and 20% for acrylic. Modacrylic appears in fake fur, wigs, and children’s sleepwear where flame-retardant treatment is mandated by regulations such as the US 16 CFR 1615 and 1616.

Brushed polyester fleece imitates wool warmth by trapping air between raised fibres on the fabric surface. The garment weighs 200 to 400 g/m² compared with 300 to 500 g/m² for a similar wool jumper, and dries in a fraction of the time. It also generates static charge in dry indoor air because its moisture regain is close to zero. A tag reading 100% polyester with the descriptor fleece or sherpa describes this construction.

Blends of 50% wool and 50% acrylic split the difference on warmth, price, and pilling behaviour, and are common on mid-market jumpers where a full-wool label would push the price outside the intended range. A wool percentage below 20% typically indicates the wool is a marketing accent rather than a functional component: the finished fabric behaves as an acrylic or polyester garment with a hint of wool character. The burn test is the fastest way to confirm what is on a tag when a label is missing. Wool self-extinguishes and leaves a brittle, crushable ash smelling of burnt hair. Acrylic melts, drips, and burns with black smoke. Polyester melts to a hard bead. A single carefully clipped fibre snipped over a metal saucer is enough to reveal the fibre family.