Wool fibres are covered in microscopic scales, like roof tiles. Warm water lifts them, movement locks them into each other, and the garment shrinks — permanently, because the fibres are now physically hooked together.
Almost every rule about washing wool follows from that one fact. Which means you can stop memorising the rules and just remember the reason.
What actually matters
- Cold water. Not because heat dissolves wool, but because it opens the scales.
- No rubbing, no wringing. Agitation is what does the damage. Press the water out between two towels.
- Dry flat. A wet jumper on a hanger stretches at the shoulders under its own weight and never comes back.
- A wool detergent, or none. Ordinary detergent is alkaline and strips the lanolin that makes wool wool.
Wash it less
Wool resists odour on its own — the fibre absorbs moisture into its core rather than holding it on the surface where bacteria live. A jumper worn once a week rarely needs washing more than twice a season. Air it overnight and it will usually be fine.
This is not thrift advice. Every wash is a small amount of damage, and the garments that last are the ones that get washed least.
When it goes wrong
A jumper that has shrunk slightly can sometimes be persuaded back: soak it in cool water with a capful of hair conditioner, which relaxes the fibre, then reshape it flat and let it dry. It works about half the time and is worth trying before giving up.
If it has felted properly — gone stiff and dense, with the knit structure no longer visible — that is chemistry, and it is not coming back.
