How long does a helmet last?

[OakLeaf]

As I said in the other thread, I have a very hard time believing EPS doesn't degrade, when I've personally plucked crumbling coffee cups off the ground pretty much every time I've done park cleanup, and it's not unusual for me to just encounter them on trails and pack them out. If EPS doesn't degrade, why are those cups crumbling? The beads themselves may not degrade (though they sure seem spongy), but the bonds between them unquestionably do.

If I replace my $60 helmet every three years, it's costing me a nickel a day. Three cents a day, if I replace it every five years. A $300 helmet replaced every three years works out to a quarter a day. I've had one concussion, wearing a helmet, and I don't want to think about what might've happened if the helmet had failed. It's worth three cents a day to me, not to find out.