An article of headwear includes a crown and a bill. The bill defines an inner edge that is operably coupled to the crown. The bill projects away from the crown and terminates at an outer edge. The bill includes a stiffener that stiffens the outer edge. The stiffener is spaced from the crown to define a cavity within the bill between the stiffener and the crown. The stiffener has a first longitudinal end that is adjacent the inner edge, a second longitudinal end that is adjacent the inner edge, an intermediate portion that is disposed between the first longitudinal end and the second longitudinal end, a top side, and a bottom side. A cross section of the stiffener is substantially constant in the intermediate portion between the first and second longitudinal ends, and one of the top and bottom sides is flat in cross section.