Nightcap (garment)

[1] From the Middle Ages to the 20th century, nightcaps were worn in Northern Europe, such as the British Isles and Scandinavia, especially during the cold winters before central heating became available.

[1] People often tended to think that cold air was harmful and unwholesome to health, so a nightcap protected them, especially if they had a receding hairline or sensitive head, etc.

[4] Some women still wore nightcaps, similar to mobcaps, to protect their elaborate curly hairstyles that were fashionable.

Nightcaps are less commonly worn in modern times, but are often featured in animation and other media, as part of a character's nightwear.

[5] The hat has become typical nightwear for a sleeper especially in comical drawings or cartoons along with children's stories, plays, and films; for example, in several Lupin III animations Daisuke Jigen has worn one as a continuation of the "hat covering eyes" gag, and in The Science of Discworld Rincewind has one with the word "Wizzard" stitched onto it.