We spend a third of our lives asleep, but pillows can be the enemy. Cotton...

https://yenkee-wiki.win/index.php/Why_Do_My_Curls_Lose_Definition_Overnight%3F_The_Truth_About_Your_Sleep_Routine

We spend a third of our lives asleep, but pillows can be the enemy. Cotton causes friction, leading to breakage and frizz. Try a silk pillowcase, or simply secure your hair in a loose, low plait before bed to minimise overnight damage