Cashmere is the warmest for its weight, which is exactly why it is often the wrong choice indoors. It is at its best outdoors in genuine cold, or in a lightweight gauge worn alone. Merino is the most versatile: fine merino regulates temperature, resists odour and can be worn against the skin without itch, which makes it the best single choice for a variable day and for travel. Wool more broadly holds shape better than cashmere and takes more abuse. Cotton knits handle mild weather and warm rooms, and they breathe well, but they hold moisture and sag over time under their own weight. Linen and cotton blends belong to spring and to air conditioning. The mistake most people make is buying heavy cashmere for a heated office and then wondering why they are uncomfortable all winter. Buy the fibre for the temperature you will actually be in.

Hold the knit up to light. A dense knit blocks most of it; a thin one glows and will pill and stretch faster. Rub the surface briskly with your palm for a few seconds, and if a haze of loose fibre appears immediately, it will pill in weeks. Check the ply if the label states it, since two-ply cashmere is meaningfully more durable than single ply at the same gauge. Look at the seams and the ribbing at the cuff and hem: tight ribbing that springs back keeps the shape of the whole garment. On cotton, check the weight, because a light cotton knit with a wide neck will grow with every wear. Country of origin tells you less than construction does. And ignore the word luxury on a swing tag entirely, since it means nothing about fibre length or twist.

Wash less than you think, and never on a hot cycle. Most knits need airing rather than washing, and a cold hand wash or a wool cycle with a wool-specific detergent three or four times a season is enough. Never hang a knit, because the shoulders will stretch into points. Dry flat on a towel and reshape while damp. Use a fabric comb or a proper pill shaver rather than picking at pills, which pulls the fibre. Store folded with cedar rather than mothballs, and store clean, since moths are drawn to the traces of skin and food rather than the wool. If a knit does snag, do not cut the loop, pull it through to the inside with a needle.

Buy one very good merino before you buy any cashmere. It will get worn ten times more often, it survives being packed and rained on, and it is the piece that quietly holds a wardrobe together. Cashmere is worth it in a real coat-weather climate and worth very little in a warm office. Do not buy a single-ply cashmere at a suspiciously low price, because you are buying short fibres that will pill into felt by February. If you take one thing away: hold it up to the light before you buy it, because density predicts how the knit will look after twenty wears better than the fibre on the label does.