The Ribcap is a soft, flexible cap – part beanie, part helmet – that hardens on impact to protect the head from damage. The secret lies in the use of some clever new molecules in a tech called d3o, which lock together when hit and absorb the shock. Neat indeed. More here.
That’s neither beanie nor helmet, but a scrum-cap.
It’s what forwards (and some backs) wear in rugby to cushion impacts, and especially to prevent cauliflower ears.