The bicorn hat that became synonymous with Napoleon is just a broad brimmed hat with the front and back folded together and pinned. From the front it looks a bit like the Sydney Harbour Bridge. It became so strongly identified with Napoleon that in some English caricatures only the hat was drawn and the reader knew exactly who was being ridiculed.
So beloved of this style of hat, Napoleon had around 170 made for him and he wore it until the day he died. He took four hats with him when he went into his final exile and one of these is still with him in his coffin in Paris but another can be seen in Napoleon: Revolution to Empire.