The short answer
A silk or satin pillowcase, and hair loose or in a loose plait rather than a tight band. Friction over eight hours does more than people realise.
- Silk or satin pillowcase. Cotton grips the hair and causes friction every time you turn over.
- Loose plait or a loose bun held with a fabric scrunchie rather than a thin elastic.
- Never sleep with wet hair in a tight style, which combines the two worst factors.
- Avoid thin elastic bands with metal joins, which cut into the shaft.
What will ruin it
Tight styles worn habitually can cause traction alopecia, which is hair loss at the hairline from sustained tension. It becomes permanent if it goes on long enough, and it is entirely preventable.
Why it works
Hair damage is cumulative friction and tension. Eight hours a night against a rough surface is a substantial share of the total mechanical stress hair receives.
This is general information, not medical advice, and it does not replace a GP, a pharmacist or NHS 111. Call 999 in an emergency. Full disclaimer.