Hats made of rogożyna- braided underwater parts of specific specie of reed.

Extremely hard and durable are probably the best idea for your headgear in sunny days. They also perfectly protect from the rain- can be used as umbrellas.

Widely dating, but “bell shape hats” were the most popular in XIIIth century (Maciejowski's Bible 1250) Can be easily found in iconography  of XIIIth, XIVth, XVth and XVIth century.