Bob Hope tipping his Pith Helmet

Pith helmets traditionally denote white Europeans chopping and slashing their way through the tropics and as a sign of imperial power starting in the late 19th century.  Using a technology developed by the French towards the end of the 19th century in Vietnam (then known as French Indochina), real pith helmets are made from the white pith of an Indian swamp plant, the sola.  Through a process of lamination, layers of the pith are glued together to make a lightweight, durable, and very strong hat.

Furthermore, because of its absorbant nature, it can be fully immersed in water to keep the wearer cool as it dries.  Since pith is also very strong, the helmets do not lose their shape or solidity as they dry, still providing very good protection.

The first helmets appeared as early as the 1840s and the traditional form developed during the 1870s.  It was used around the world and even made an appearance in the US Southwest during the 1880s.  True pith helmets were used extensively during World War One in tropical areas but by the Second World War, while still a popular style, many of the helmets were no longer made of traditional pith materials.  These sun helmets (many made of plastic or straw) are still in use today throughout the world by a range of people, including USPS postal workers during the summer and the Thai Royal Guards.

For the real article, you can get pith helmets online.