Among the family of sun helmets, they are called differently according to its materials. Pith helmet for ones made by wickerworks of sola pith originally found in India and Southeast Asia. Cork helmet for ones made of oak cork, Felt helmet for ones made of leather felt or hard leathers (especially Prussian and German pickehaube). yet there's one.
Fiber helmet !!
Clearly it is a helmet made by fiber plastics, I believed that it is introduced in 1930s with the introduction of different types of polymers created/discovered by petrochemical industry. Brazilian is (possibly) the first nation to make its sun helmets out of fiber plastics
http://www.nyc-techwriters.com/militaria/brazilian_helmets.htm
This website claimed that this helmet is ballistic proofs as well as it is waterproof. by 1930s the ballistic characteristics are quite doubtful to me. though early ballistic vest has been introduced by then. and it is made of multilayer clothes of some kind. yet it wasn't common i think.
Another example of (possibly claimed to be) fiber helmet was ones worn by NVA troops of every ranks.. NVA from Vietnam War. though originally made of wickerworks of either pith or bamboo (or any vegetations that can make baskets), the plastic (some said it's fiber plastics) versions are more common, and it's still being manufactured today! and you can see it in headgear stores / sourveinior stores in Thailand too!
^ Traffic cops in Hanoi still wear it today
^ Actually it's made in China

Chinese troops rarely wear ones but Vietnamese troops do! it doesn't really shellproof but they don it. in 'We were soldiers' movie you'lll see how weak this helmet is. well unless it was made of Kevlar
so what actually is 'Fiber Helmet' and name the 'fiber plastics' that made ones please.
Also did Brazilian examples bulletproof? the Modern PASGT is sometimes referred to as 'fiber helmet' , though Kevlar Helmet name is more common