One reason that people cite for disliking bicycle and motorcycle helmets is that they wreck one’s hairdo.
It seems a small price to pay to keep your cranium intact but today’s invention attempts to reduce this disincentive by preserving the shape of one’s hair.
A composite outer shell would contain a layer of impact-absorbing foam, as usual. This layer would have radial holes in it. In each hole, a stiff, round-ended rubberised prong would be free to slide.
Depressurising the rear face of the foam, using a small bladder, would cause all the prongs to withdraw. The helmet could be donned and the foam repressurised.
This would cause the huge number of prongs to move radially inwards, making contact with the wearer’s scalp but without disturbing their coiffure.
The prongs would all lock in position, providing improved fit and thus excellent impact force distribution in the event of an accident.
To remove the helmet, depressurise the foam once more.