Top hats were a fashion must for all respectable gentlemen for a good portion of the 19th century. However the felted beaver fur that was traditionally used in construction proved just slightly too hot for the summer months.
The solution was the introduction of straw top hots for summer wear. In the very early 19th century some were even painted black to resemble their winter counterparts as closely as possible, but eventually leaving the straw its natural color became the style of choice. This one is American in origin and dates to 1832.