A mob cap or mob-cap is a round, gathered or pleated cloth (usually linen) bonnet consisting of a caul to cover the hair, a frilled or ruffled brim, and (often) a ribbon band, worn by married women in the Georgian period, when it was called a "bonnet". Originally an informal style, the bonnet became a high-fashion item as part of the adoption of simple "country" clothing in the later 18th century. It was an indoor fashion, and was worn under a hat for outdoor wear. During the French Revolution, the name "Mob Cap" caught on because of the poor women who were involved in the riots wore them, but they had been in style for middle class and even aristocracy since the century began.
By the Victorian period, mob caps lingered as the head covering of servants and nurses, and small mob caps, not covering the hair, remained part of these uniforms into the early 20th century.
Modern versions of mob caps are still worn in the medical industry, in cleanrooms, and in other sectors where the hair has to be contained. These mob caps are usually a simple circle shape with an elastic band and may be made of disposable materials such as spunbound polypropylene or of nylon netting.