"Louise Bremner" wrote ...
> Paul Blay <ranma@saotome.demon.co.uk> wrote:
>> 
>> Quite hard to make a _good_ hard hat.  To do it's job properly it has to
>> absorb a lot of energy (typically in non-elastic deformation).  If it's
>> /just/ hard it passes on too much of the impact to its wearer.
> 
> Um... Do you mean non-elastic deformation? 

Yes I do.

> You wouldn't want it to fail
> in a brittle fashion at the first impact, would you?

Not 'fail' but many (most?) hard hats are designed specifically to be used 
'in anger' _once_. Just like the 'crumple zones' on cars etc.  You can absorb 
a lot more energy that way.  Typically you'd have an outer shell that probably 
does deform elastically but the stuff that 'does the business' is the padding
inside.
 
> And I could wonder just how well some of those cheapie hard hats that
> I've seen on sale could absorb energy....

Well I did say '_good_ hard hat'.