Originally Posted by
rydabent
If you fall or are knocked off your bike and your head hits a sharp object that penetrates a foam helmet, you could be killed. A hard shell helmet like the Tourlite might prevent that.
A thicker, harder helmet shell probably could do a superior job of resisting sharp penetrating objects impacted in a collision. If sharp objects were something helmet test engineers thought people that ride generally needed to have protection against in a collision, maybe they'd test helmets for this, and so encourage bike helmet manufacturers to design helmets to resist that type of impact. The following link leads to a page with pictures of a test rig engineers use to test helmets, also showing the test objects or 'anvils' helmets are dropped onto:
http://www.helmets.org/testing.htm
"...The hazard or curbstone anvil is rounded like the edge of a curb...", is about the sharpest object the CPSC in these pictures, appears to test for.