[kolektiv]

Also, (can't read the article but assuming some kind of context), even if the styro compressed rather than shattering - that's still energy being used for something which isn't cracking your skull. It still seems like it would be beneficial.

If the author is claiming that once it's compressed it won't be as good next time, then that's insane - helmets aren't supposed to be re-used after accidents (whether bike, motorbike, or car racing - I've had to sadly replace my motor racing helmet after an incident, and it's a lot more than buying a new bike lid - but you still do it without flinching because it's your brain on the line here).

[omaranto]

If the author is claiming that once it's compressed it won't be as good next time, then that's insane - helmets aren't supposed to be re-used after accidents

Why is it insane to think it won't be as good next time? Isn't that exactly the reason you are not supposed to re-use them?

[Lewton]

Full paragraph:

"People will so often put up photos on social media of obliterated helmets and say, “Holy crap, look at my helmet! It saved my life!” But helmets are not supposed to shatter. When a helmet protects your head from a serious injury, the styrofoam inside will be compressed and stay that way. Most of the pictures I’ve seen are of helmets that have broken apart. It’s likely that the helmet did not protect someone from a severe injury."

[kolektiv]

In which case yes, just a very misinformed original author. Shattering, cracking, etc. are all known, planned features of a helmet impact - anything which can absorb energy in the helmet and not the head is a good thing (with some obvious caveats of course).

[moopling]

Depends, depends... Fracturing of a flaw requires much less energy than plastic deformation. So it is really a question of whether it deformed first and then cracked, or fractured early. In the latter case, possibly caused by a flaw or very sharp impact, not much energy would be absorbed at all!