Satin bonnet
A loose satin or silk cap worn at night to protect hair from friction and keep a style in place.
Also: sleep bonnet, silk scarf
A satin bonnet is a loose cap of satin or silk worn over the hair at night. Smooth fabric rubs less against the hair than cotton pillowcases, so curls, braids and blowouts keep their shape and the hair loses less moisture. Bonnets and night scarves are a long-standing part of hair care among Black women. The same idea gives silk pillowcases and the pineapple, a loose high ponytail for sleeping.