This particular Fedora due to its lightness both in weight and colour plus open its weave should be more accurately called a Panama Hat.
This particular Panama is made of hessian I think and probably stiffened with some sort of starch paste or glue but since purchased second hand and not detailed on any sort of label its really a guess
The loose weave and holes in the crown and make this a cooling hat for humid summers, designed to protect against the sun rather than other elements such as rain or wind.
The original Panama hats date back as far as 16th Century and originate in Ecuador where they were made from plated palm leaves. The traditional Ecuadorian toquilla hat is protected by its heritage status.
Never made in Panama the hat gots name mainly due to president Theodore Roosevelt's wearing one on his trip to oversee the construction of the Panama Canal.
Purchase for £8 including carriage off an auction site called clutter buys.