Cotton pillowcases cause friction, leading to breakage and frizz. Swap to silk...

https://wiki-view.win/index.php/Why_Your_Pillowcase_is_the_Missing_Piece_in_Your_Hair_Care_Routine

Cotton pillowcases cause friction, leading to breakage and frizz. Swap to silk for a smoother surface, or braid your hair into a loose, low plait before bed. It’s an easy habit that keeps your hair healthy and makes your morning routine much simpler.