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. EPS is a long-lived material little affected by normal environmental factors. Unless you mistreat it we would not expect it to "dry out" enough to alter its performance for many years.
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!"
We applaud MET for undertaking an actual testing program on helmet life and for making that statement. We regard it as a triumph of integrity over marketing. MET's helmets are made with industry standard shells and liners, so there is no reason we can see that their recommendation should not be good for many other helmet brands as well. If another manufacturer comes up with a testing program that shows earlier deterioration in the protection from their products we will review this page.
In sum, we don't find the case for replacing a helmet that meets the ASTM or Snell standards that compelling if the helmet is still in good shape and fits you well.