Proven, helmets expanded polystyrene (EPS) foam doesn't wear out in 3-5 yrs.

[98valk]

so the testing was done on bicycle helmets however the exact same expanded polystyrene (EPS) foam is used for both types of helmets. motorcycle helmets have much thicker expanded polystyrene (EPS) foam than bicycle helmets due to the chances of impact at much higher speeds. still testing shows the protection of expanded polystyrene (EPS) foam does not deteriorate with age.

This is the first time anyone has applied rigorous science to assessing the effects of age on helmet foam liners. It is a welcome antidote to the strident marketing claims that foam deteriorates with age.

https://pubmed.ncbi.nlm.nih.gov/26902784/

Age Does Not Affect the Material Properties of Expanded Polystyrene Liners in Field-Used Bicycle Helmets
Foam cores were extracted from 63 used and unused bicycle helmets from ten different models spanning an age range of 2-20 yrs. All cores were impact tested....
Based on these data, the impact attenuation properties of EPS foam in field-used bicycle helmets do not degrade with the age.

https://helmets.org/helmetlineraging.htm

MEA Forensic announced at a May 2015 ASTM F08.53 technical meeting the results of their testing of 675 bicycle helmets, some as old as 26 years. "There is no justification for two to ten year replacement recommendations based on impact performance," said MEA's Alyssa DeMarco.

In 2016 MEA published this study in a peer-reviewed journal, the Journal of Biomechanical Engineering. The abstract is free, but the article costs $25. Similar data was published in 2017 in the Annals of Biomedical Engineering, with a cost of $40.

This is the first time anyone has applied rigorous science to assessing the effects of age on helmet foam liners. It is a welcome antidote to the strident marketing claims that foam deteriorates with age.

[luftkoph]

Interesting

[WintrSol]

I thought the problem was that the shell deteriorated with age, though.

[98valk]

I thought the problem was that the shell deteriorated with age, though.

I have 20 yr old HJC that I use during colder temps now. nothing wrong with it. most of the protection is from the EPS. 
shell deteriorating?, another story to sell helmets??
plenty of other forums out there addressing the shell age story. advrider.com has a few threads on the subject. I tend to remember a lot of discussion was about a certain type of shell material which wasn't always used and even then only for a short time.

I'm all ears if u find any additional info.   

[WintrSol]

shell deteriorating?, another story to sell helmets??

That's probably the real story. Never saw any testing done.

[Gondul]

Found basically the same info...

I'll just be replacing the 'comfort' padding to make sure it stays nice and snug.
Otherwise, unless there is some new tech/advancement which improves the protection performance of the helmet I currently have or I actually end up having to use it to protect my nugget, I'll be keeping this one for a while.

[Jess from VA]

I had a Bell Magnum 3/4 helmet i wore with my DT360 motocrosser (early 70s), and wore it off and on for 35-40 years.  When the spiders moved in, I pitched it.

They changed my favorite EXO100 Scorpion (did away with the neck curtain for cold weather) so I've been wearing it for 12 years or so.  The visor blew off in a storm a few years back.

I'm real particular with helmet fit.  If it's not just right, I don't want it. (oval, not round).

[SPOFF]

The honest truth is I replace helmets because I want a new helmet. I currently have seven. As for newer technology, if you own one of the newest ECE rated helmets you will discover it is as big as a house. I look like Dark Helmet from Space Balls. My 2020 Snell helmets are a bit more of a reasonable size.