Wool, Explained: Merino, Lambswool, Worsted and Woollen, and Why the Same Fibre Makes a Suit and a Jumper

Wool is the only fibre that shows up in a summer suit, a winter coat, a running base layer and a carpet, and the labels on all four use words that sound like grades and are not. Merino and lambswool describe the sheep and the shearing. Worsted and woollen describe the spinning. Super 100s and 150s describe fineness. None of them, on its own, tells you whether the garment will last, and a shopper who understands what each word is measuring buys better than one who assumes higher is better. The Woolmark Company, the Australian growers' body, publishes the technical standards behind most of it; the rest is trade custom.

The sheep

Merino is a breed, originally Spanish and now overwhelmingly Australian and New Zealand, whose fleece is fine: fibres of 17 to 24 microns in diameter, against 30 or more for a hill sheep. Fineness is what makes it soft against skin, which is why almost all wool that touches skin directly, base layers, fine knitwear, suiting, is merino. Lambswool is the first shearing of any breed, at around seven months, and is softer than the same animal's later fleece because the fibre tips have never been cut. Shetland is a breed and a place; a Shetland jumper made in China from other wool is legal in most markets and common. Cashmere and mohair are goat, alpaca is camelid, and we have covered cashmere on its own.

The spin

This is the distinction that matters most and is explained least. Worsted yarn is made from long fibres combed parallel before spinning, giving a smooth, dense, strong thread. Woven, it becomes suiting, gabardine, flannel's crisper cousins; it drapes, holds a crease, resists pilling and shines with wear. Woollen yarn (the spelling is the trade's) is carded, not combed, leaving short fibres every which way, and is spun with more twist and more air. It is loftier, warmer for its weight, softer, and pills, because the short ends work loose. Tweed, most knitwear and blankets are woollen-spun. A merino jumper can be either, and the worsted one will look neat for years while the woollen one will be warmer and bobble by March. Neither is wrong.

Super numbers

Super 100s, 120s, 150s on suiting refer to fibre fineness on an old English scale; higher is finer, softer and more expensive. It is also weaker and creases more. A Super 110s cloth is a sensible daily suit; a Super 180s is a special-occasion cloth that will bag at the knees if worn to the office. Weight, quoted in grams per metre or ounces per yard, tells you more about how a suit will wear than the Super number does: 260 to 300 grams is a year-round weight in temperate cities, under 240 is summer, over 340 is a winter cloth.

What lasts

For durability, look for a tight weave or knit, a slightly coarser fibre, and a woollen-spun yarn in knitwear that has been fully fashioned rather than cut and sewn. For softness, go finer and accept the trade. For warmth per gram nothing woven beats a woollen-spun cloth with the air still in it. Wool of any grade is naturally odour-resistant, which is why a merino T-shirt can be worn for days, and flame-resistant, which is why it is on aircraft seats. It is also food for moths; cedar does little, cold and cleanliness do more, and a garment put away dirty will come out holed. Read our guide to judging a garment for the construction side. The fibre is only half the story.