The kettle helm was the staple of medieval headgear. Worn primarily by footmen and gaurdsmen in the 1100s, this brimmed metal helmet ("Chapel de Fers" or "iron hats" as the French called them)provided adequate protection while allowing excellent vision and mobility. They were also fairly light and could be worn for long periods without incurring fatique. There's also some anecdotal evidence that soldiers would actually cook stew iinside the helmet when they had no pots and pans. Not sure if it's true or not, but seems plausible enough.
It was strongest against attacks from above, like, say from sociopathic knights on horseback swinging swords or warhammers......read more