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.