^ my personal bet is that helmets do degrade a bit over time, particularly with use. UV rays are said to have an effect. Dropping them, and throwing them in hot trunks can't be a positive. Chemicals and sweat may have an effect.

All that said, my bet is an 8 year old helmet that hasn't been crashed is dramatically better than no helmet.

I keep a couple of old helmets like that around in the Garage in case a guest wants to ride. Never felt unsafe with them using them.

But for my own use, I typically am going to want a nice new helmet before the current one gets old enough to worry about its integrity.