If Snell says that I am disappointed. Breaks down quicker with wear sure but it still breaks down with age - temp matters too. Used to cut people a break if they had a receipt but got lied to too often
I think he was saying it only saves your life if you’re actually wearing the helmet instead of it being locked on the side of the bike while you’re riding or such
I've had several helmets that sat nearly unused on a shelf in the garage for several years and can attest that given enough time the polystyrene foam degrades. Seen it myself. I have no idea where that Snell report was acquired but I'm quite skeptical.
http://biomechanical.asmedigitalcollection.asme.org/article.aspx?articleid=2497744 https://www.helmets.org/helmetlineraging.htm I think it's just a general recommendation. Surely aging occurs. Don't really think the polystyrene has any real appreciable degrading, but maybe everything else holding it together does. That and advances in materials, etc etc. Either way, who doesn't want a cool looking lid, not something your dad wore in the 50's.