> a concrete helmet is literally worse than useless.
Is it? It would still absorb energy upon impact. Which, in contrast to popular belief about bike helmets, is its main function. Yes, ordinary bike helmets will also just break. But in doing so, they absorb energy which then won't be absorbed by your skull.
There is no point in a perfectly stiff helmet. It would just transfer the energy right through and you'd crash your skull into the helmet, which doesn't help.
Is it? It would still absorb energy upon impact. Which, in contrast to popular belief about bike helmets, is its main function. Yes, ordinary bike helmets will also just break. But in doing so, they absorb energy which then won't be absorbed by your skull.
There is no point in a perfectly stiff helmet. It would just transfer the energy right through and you'd crash your skull into the helmet, which doesn't help.