A boater (also straw boater, basher, skimmer, cady, katie, canotier, somer, sennit hat, or in Japan, can-can hat) is a kind of summer hat worn by men, regarded as somewhat formal, and particularly popular in the late 19th century and early 20th century.
It is normally made of stiff sennit straw and has a stiff flat crown and brim, typically with a solid or striped grosgrain ribbon around the crown. Boaters were popular as summer headgear, especially for boating or sailing, hence the name. They were supposedly worn by FBI agents as a sort of unofficial uniform in the pre-war years. It was also worn by women, often with hatpins to keep it in place. Nowadays they are rarely seen except at sailing or rowing events, period theatrical and musical performances (e.g. barbershop music) or as part of old-fashioned school uniforms. Since 1952, the straw boater hat has been part of the uniform of the Princeton University Band, notably featured on the cover of Sports Illustrated Magazine in October, 1955. Boaters are also a part of the traditional and persisting garb of barbershop quartets. Recently, soft, thin straw hats with the approximate shape of a boater have been in fashion among women.
The boater is a fairly formal hat, equivalent in formality to the Homburg, and so is correctly worn either in its original setting with a blazer, or in the same situations as a Homburg, such as a smart lounge suit, or with black tie. John Jacob Astor IV was known for wearing such hats. Actors Harold Lloyd and Maurice Chevalier were also famous for their trademark boater hats.
Inexpensive foam or plastic skimmers are sometimes seen at political rallies in the United States.