Like linen, buying cashmere is a matter of discovering the important metrics and discarding the unnecessary.

The truth about quality cashmere is much more complex than simply looking for that pure cashmere label.

Pure is not an absolute term. The finest cashmere consists only of the whitest, longest, thinnest hair from the underfleece, whereas lower-quality cashmere may be either the shorter, coarser hair from the undercoat–typically from the rear end of the animal rather than its belly–or, more dubiously, shorter hair that has either not been properly dehaired or, worse still, blended with yak or rabbit hair. […]

Yet even cheap cashmere can feel lovely. It’s hard to know, as you queue at the till, whether your bargain will pill or sag within days. (Pilling afflicts expensive cashmere too, though it should stop after the first wash.) But there are subtle signs of quality, and once you’ve got your eye in, much of the cheaper cashmere on the market starts to seem a false economy.

Look for tension in the knitting: stretch a section and it should ping back into shape. Hold it up to the light and you shouldn’t see much sky: paradoxically, the best cashmere, though made from the finest hair, has a density to it. Examine its surface: fluffiness suggests the yarn was spun from shorter, weaker fibres and will pill. Be sceptical about softness, too. Over-milling can make a garment too soft and silky, and therefore prone to bobbling and losing its shape. More expensive cashmere may be harder to handle in the shop, but will ease up with wear and hand-washing. The best cashmere actually improves with age–so long as the moths don’t get to it.