Courtesy of Wikipedia
The style can be traced back to the 14th century in United Kingdom and parts of Italy, when it was more likely to be called a “bonnet”, which term was replaced, except in Scotland, by “cap” before about 1700. When Irish and English immigrants came to the United States, they brought the flat cap with them. This style of cap is also referred to in some parts of the UK as a cheesecutter cap because of its wedge shape.
A 1571 Act of Parliament to stimulate domestic wool consumption and general trade decreed that on Sundays and holidays, all males over 6 years of age, except for the nobility and persons of degree, were to wear caps of wool manufacture on force of a fine (3/4d (pence) per day). The Bill was not repealed until 1597, though by this time, the flat cap had become firmly entrenched in English psyche as a recognized mark of a non-noble subject; be it a burgher, a tradesman, or apprentice. The style survives as the Tudor bonnet in some styles of academic dress.
Flat caps were almost universally worn in the 19th century by working class men throughout Britain and Ireland, and versions in finer cloth were also considered to be suitable casual countryside wear for upper-class English men (hence the contemporary alternative name golf cap). Flat caps were worn by fashionable young men in the 1920s.
The stereotype of the flat cap as purely “working class” was never correct. They were frequently worn in the country, but not in town, by middle and upper-class males for their practicality. Mather says: “A cloth cap is assumed in folk mythology to represent working class, but it also denotes upper class affecting casualness. So it is undoubtedly classless, and there lies its strength. A toff can be a bit of a chap as well without, as it were, losing face.” The British workman no longer commonly wears a flat cap, so in the twenty-first century, it has gained an increasingly upper class image.