What is a "nightcap"?

A nightcap is a soft, warm hat worn while sleeping to keep the head and ears warm. Typically made of cotton or flannel, nightcaps can be cone-shaped or cylindrical and often have a tassel or pom-pom at the end. They were popular in the 18th and 19th centuries and were worn by both men and women. In addition to keeping the head warm, they were also thought to have health benefits, such as preventing illness and aiding in sleep. Nightcaps have since fallen out of fashion and are now primarily used as a novelty item or in costume design.