A mushroom hat (also sometimes referred to as a mushroom brim hat or dish hat) is a millinery style in which the brim of the hat tilts downwards, resembling the shape of a mushroom (or dish). It is a style that first emerged in the 1870s and 1880s, when it was usually made of straw. It became fashionable again from around 1907 to the late 1920s; these versions featured a distinctly downturned brim although the size and shape of the crown varied according to prevailing fashions.
A new and exaggerated version of the mushroom hat was popularised by Christian Dior in 1947 as part of his "New Look" collection. This style generally had a minimal crown and a very wide brim, with some models resembling a flying saucer.