Smart move. Helmet makers, retailers and others have been suggesting a 5-year expiration on helmets but that's just not the case. Old
undamaged helmets are at least as good as new ones. Here's some information published in the Journal of Biomechanical Engineering. Basically, it shows that old helmets (up to 26 years old) without damage provided protection.
Helmet Impact Performance Proven to Hold Up for Decades
There are reasons to replace your helmet, but simple age is not one of them.
Extensive testing of used (but not crashed) bicycle helmets shows that the foam liners retain their performance over many years. MEA Forensic announced at a May 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.
MEA and collaborator Collision Analysis collected 1,500 used helmets from consumers and eliminated any that showed damage or did not have date of manufacture stickers. The helmets studied had dates that ranged from 1987 to 2013. They crash tested them at 3 m/s (a drop of 1.5 ft.) and 6.2 m/s (a drop of 2 meters--the CPSC standard drop) on a flat anvil in the dry ambient condition. There were only four that exceeded the 300g maximum threshold: three of the oldest models made to meet only the old ANSI standard, and one newer model that had been recalled. So 671 of the helmets passed the current CPSC impact performance standard.
MEA's analysis showed that there was no significant impact performance change with age. Their 26 year data including all 675 helmets tested produced only a 0.7g per year increase in impact readings at the higher drop height. On average, road helmet models produced results 40g lower than skate-style models, and extra-small helmets were 21g lower than large helmets. Lower g's registered in the headform means less shock passed through to the head, but since they are averages they may not apply for a particular helmet model.
After crash testing the helmets on a standard test rig, MEA took core samples from an uncrashed area of 63 of the helmets and tested them at the equivalent of a 6.2 m/s helmet impact. This generated data based solely on the foam performance. They collected stress and strain data related to aging of the foam. Again, the findings indicate that helmet liner foam does not deteriorate with age.
MEA usually publishes their studies in a peer-reviewed journal, but that can be a slow process.
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. There are other reasons to replace a helmet--crash damage, strap deterioration, improving fit--but simple aging of the foam liner is not one of them.
April, 2016 - the study is now published in the Journal of Biomechanical Engineering