The tam o’ shanter is a flat bonnet, originally made of wool hand-knitted in one piece, stretched on a wooden disc to give the distinctive flat shape, and subsequently felt. The earliest forms of these caps, known as a bluebonnet from their typical color, were made by bonnet-makers in Scotland. By the year 1599 five bonnet-makers guilds had formed in cities around the country: Edinburgh, Aberdeen, Perth, Stirling, and Glasgow. At the end of the sixteenth century, it was said that a tam hat look like the normal fashion of men and servants.
Similar in outline to the various types of flat bonnet common in northwestern Europe during the 16th century, the later tam hat is distinguished by the woolen ball or cookie decorating the center of the crown; the name itself did not enter common usage until the early 19th century, subsequent to the popularity of Burns’ poem. The term came to denote a hat, usually associated with Scottish military regiments, derived from the old bonnet, along with the Glengarry and the Balmoral bonnets. The Balmoral was sometimes simply described as synonymous with the tam o’ shanter.
Before the introduction of inexpensive synthetic dyes in the mid-19th century, the Scottish knitted bonnet was made only in colors easily available from natural dyes, particularly woad or indigo (hence “bluebonnet”).
Women have also adopted a form of this hat, known as a “tammy” or “tam”.