I recently listed 2 helmets in good condition on the classifieds and was asked a question as to their age by one reader due to them possibly having expired. I was a little oblivious about the topic so I went looking for some studies that actually tested this and not just normal manufacturer talk trying to sell more gear. I am including the links below but curious as to others experience? Also, just a caveat, this is not discussing helmets that have taken big hits.
https://link.springer.com/article/10.1007/s10439-017-1842-4
https://asmedigitalcollection.asme.org/biomechanical/article-abstract/138/4/041005/371203/Age-Does-Not-Affect-the-Material-Properties-of?redirectedFrom=fulltext
