Cotton pillowcases create friction that leads to breakage and morning frizz....

https://wiki-club.win/index.php/What_Kind_of_Hair_Tie_Should_I_Avoid_at_Night%3F_The_Beauty_Editor%E2%80%99s_Guide_to_Protecting_Your_Strands

Cotton pillowcases create friction that leads to breakage and morning frizz. Swapping to silk helps, but a loose braid or silk scrunchie is just as effective. Protecting your hair overnight is a simple habit that makes styling much easier once you wake up