Mob Cap refers to a large women's indoor cap covering all the hair which was worn in the 18th and 19th centuries. Mob Cap also refers to a woman's linen nightcap which later in era h ad pleated border worn under large bonnet hats.
Mob Cap was undress headwear; becoming popular in the 1730's and worn in some form into the next century. It had a puffed crown placed high on the back of the head, a deep flat border surrounding the face, and side pieces carried down like short lappets, which could be left loose, pinned, or tied under the chin. The flat border usually was frilled or had lace.
Mob Cap had gathered ruffle around edge, which was later referred to as a Dust Cap