at the moment helmets in game are just a skin, helmets dont have any bonus or nothing, it would be really nice and realistic that helmets become a item like others in game, for example backpacks or granade bags, of course gaijin should add a new solt for helmets.
of course like any other item you should buy it with bronze orders, soldiers should start with no helmets, it would be nice its there its different type of helmets like small backpacks ot big backpacks with different % of bonus.
but what bonus helmets should give to soldiers, Helmets should reduce the head damage multiplier that soldiers take, different tier or type of helmets should have +/- head damage multiplier reduction.
it does reduce damage, there was test on youtube long ago, showing that hitting head at the helmet compare to body is 180% damage, while hitting face and neck (where the helmet doesn’t covered) is 200% damage, not much different but can save you sometimes