making a light helmet handle devastating blows might well be a lot harder than you think.
First off there's a minimum thickness of EPS for safety to be achieved,
there goes super aero.
Then there's a shell that's strong enough to distribute impact over a larger EPS area, but not so strong that it doesn't absorb energy.
There goes light, or your pricetag, pick one.
If I were designing a helmet for
DH, it would have more foam on the back than it has on the sides. (heelside highsides are the worst)
and a thicker back isn't an aero problem.
It'd be injected polycarbonate, and have ablative aero parts.