Basically the EPS (the polystyrene bit) hardens at the rate of about 5%/year so after three years the helmet has lost 15% of its ability to absorb impacts. Bear in mind that’s from the date of manufacture
That’s interesting. Anything to back it up? Contradicted by everything here –
http://www.bhsi.org/replace.htm
Occasionally somebody spreads rumors that sweat and ultraviolet (UV) exposure will cause your helmet to degrade. Sweat will not do that. The standards do not permit manufacturers to make a helmet that degrades from sweat, and the EPS, EPP or EPU foam is remarkably unaffected by salt water. Your helmet will get a terminal case of grunge before it dies of sweat. Sunlight can affect the strength of the shell material, though. Since helmets spend a lot of time in the sun, manufacturers usually put UV inhibitors in the plastic for their shells that control UV degradation. If your helmet is fading or showing small cracks around the vents, the UV inhibitors may be failing, so you probably should replace it. Chances are it has seen an awful lot of sun to have that happen. Otherwise, try another brand next time and let us know what brand faded on you.
At least one shop told a customer that the EPS in his three year old helmet was now “dried out.” Other sales people refer to “outgassing” and say that the foam loses gas and impact performance is affected. Still others claim that helmets lose a percentage of their effectiveness each year, with the percentage growing with age. All of that is nothing but marketing hype to sell a replacement helmet before you need it. There is some loss of aromatics in the first hours and days after molding, and helmet designers take account of that for standards testing. But after that the foam stabilizes and does not change for many years, unless the EPS is placed in an oven for some period of time and baked. The interior of your car, for example, will not do that, based on helmets we have seen and at least one lab crash test of a helmet always kept in a car in Virginia over many summers. Helmet shells can be affected by car heat, but not the foam. The Snell Memorial Foundation has tested motorcycle helmets held in storage for more than 20 years and found that they still meet the original standard.
Test Lab proof that performance holds up
In 2015 MEA Forensic reported on their extensive testing of used (but not crashed) bicycle helmets shows that the foam liners retain their performance over many years. Some of the helmets were as old as 26 years. They crash tested 675 helmets in their lab. Their analysis showed that there was no significant impact performance change with age. Their data including all 675 helmets tested produced only a 0.7g per year increase in impact readings at the higher drop height. After crash testing the helmets on a standard test rig, MEA took core samples from an uncrashed area of 63 helmets and tested them. This generated data based solely on the foam performance. Again, the findings indicate that helmet liner foam does not deteriorate with age. We have more on this landmark study in this Update newsletter.
An honest manufacturer: MET
The Italian company MET says in their 2010 catalog:
“We are often asked ‘For how long is a helmet safe?’, or ‘how often should I replace my helmet?”’ Until now it has been difficult to find any reliable figures to help answer these queries. MET have now developed a series of tests which are conducted on aged helmets to determine a ‘best before’ date (unless the helmet is involved in an accident. In that case it should be replaced immediately.). The results indicate that, if used properly accordingly to our owner manual, our helmets will still do their job up to eight years after they have been made. Not only is that good news for the customer, it’s great news for the environment!”
