A 2006 study showed that “280,000 people in the U.S. receive a motor vehicle induced traumatic brain injury every year” so you would think that wearing a helmet while driving would be commonplace. Race car drivers wear helmets. But since almost no one wears a helmet while driving a regular car, you probably fear that if you wore one you would look silly, attract the notice of the police for driving while weird, or the attention of another driver who took your safety attire as a challenge. (Car drivers are more likely to hit bicyclists who wear helmets.)
The $30+shipping Crasche hat is designed for people who should wear a helmet but don’t. It looks like a ski cap, but contains concealed lightweight protective material. People who have signed up for cryonics, such as myself, would get an especially high expected benefit from using a driving helmet because we very much want our brains to “survive” even a “fatal” crash. I have been using a Crasche hat for about a week.
I doubt it.
Ordinary helmets are thick. That isn't to make them stronger. Bicycle helmets are made of something like expanded polystyrene: you can push a fingernail into them. I've never worn a motorbike helmet, but they have thick padding inside.
The reason is to make space between your head and the impacting object, so that the impact forces are spread over a longer time as the helmet material deforms. Acceleration = force/time, so increasing the time reduces the acceleration.
A hard shell spreads the force of the blow over a larger area, but does nothing to reduce the acceleration.
An airbag already hits with a large area, so I don't think the Crasche would have any effect in that situation. It's a hard shell with thin padding, so I expect it is of some value against sharp objects and abrasions, but won't alleviate impact forces much. I wonder what their patent claims are.
To answer my own question, here are some of the patents. The claims consist of the design and method of making the protective inserts, not the sort or amount of protection it gives.