How to Wash Wool and Cashmere Without Shrinking or Felting Them
Wool and cashmere fail in one specific, irreversible way — felting — and almost every washing mistake with these fibers traces back to it. The fix isn't complicated once you understand what's actually happening to the fiber: keep temperatures low and consistent, skip the agitation, and always dry flat. The steps below are general guidance; if your garment's care label says something different, follow the label.
Key takeaways
- Felting is permanent: heat plus moisture plus agitation lift and interlock wool's fiber scales, and it can't be reversed.
- Wash wool at ~40°C on a wool cycle (or ~30°C by hand); keep wash and rinse water the same temperature to avoid thermal shock.
- Cashmere runs cooler than wool — treat 30°C as a ceiling, cooler is safer.
- Always dry wool and cashmere flat; never hang (stretches) or tumble dry (felts).
- Wash every 3–4 wears — wool is naturally self-cleaning.
Why Wool Felts (and Why You Can't Undo It)
Wool and cashmere fibers are covered in microscopic scales, like tiny overlapping shingles. Heat, moisture, and agitation together cause those scales to lift and interlock with the scales on neighboring fibers — and once they've locked together, they can't be pulled back apart. That's felting: the fabric shrinks, thickens, and turns dense and matted, permanently. A wool sweater that's been through a hot, agitated wash isn't damaged so much as transformed into a different, unwearable object.
The three ingredients — heat, moisture, agitation — all have to be present for felting to happen, which is exactly why wool care is built around removing at least one of them at every step.
The Wash: Temperature and Handling
- Use a wool or gentle cycle at around 40°C (104°F), or hand wash in lukewarm water around 30°C.
- Use a pH-neutral wool detergent — regular detergent is often alkaline, and alkalinity accelerates felting.
- Keep the wash and rinse water the same temperature. A sudden hot-to-cold or cold-to-hot swap (thermal shock) is itself enough to trigger felting, independent of agitation.
- Don't rub, twist, or wring. Let the garment soak (Woolmark recommends about 10 minutes), then gently press out water — squeeze, don't wring.
- Rinse from lukewarm down to cold, never the reverse.
If you're hand washing, dissolve the detergent fully before adding the garment, let it float rather than pushing it under, and agitate as little as possible — a light swish is enough.
Cashmere: Same Rules, Even Less Margin for Error
Cashmere is finer and more delicate than most sheep's wool, so the same felting mechanism applies with less room for error. Woolmark's general guidance is around 30°C, though many luxury retailers recommend going cooler — 20°C or below — for cashmere specifically. Treat 30°C as the ceiling and cooler as the safer default. Never hang cashmere to dry while wet — the fiber's own weight stretches it out of shape; always dry flat instead.
Drying: Flat, Always
Both wool and cashmere must be dried flat — never on a hanger (weight stretches them) and never in a tumble dryer (heat plus tumbling is a direct route to felting). Lay the garment on a clean towel, gently reshape it to its original dimensions, and let it air dry completely before wearing or storing it.
Between Washes
Wool is naturally odor- and dirt-resistant, so it doesn't need washing after every wear. Airing a garment out between wears and washing roughly every 3–4 wears is enough for most wool and cashmere pieces — washing less often is itself a felting-prevention strategy, since it means fewer trips through water and agitation.