UKC

Just looking for a definitive answer on this; my understanding is that the polystyrene in a helmet (not shell type helmet) degrades over time regardless of usage. The foam therefore becomes less able to absorb impact.

Is this right or nonsense? If it does degrade, over what time period does this happen? Is it material i.e. even though foam may not be as spongey / robust as it was originally does it still perform, say at 80% or something of original performance?

Thanks!

In reply to ksjs: does this help? http://www.thebmc.co.uk/Download.aspx?id=629

In reply to frankcp87: Very good document - thanks. I see in there that Petzl gives 10 years on helmets; checked the BD website and the tracer (my helmet) gets 10 years shelf life and less i.e. 8 or 5 years (depending on usage) in use.

I found this thread on a biking forum http://forums.roadbikereview.com/general-cycling-discussion/helmet-lifespan...

where somebody suggests that the whole foam degrading thing is another example of marketing / sales led information i.e. the foam's performance doesn't actually deteriorate at all.

Then I found this which is more detailed, from a triathlon forum this time http://beginnertriathlete.com/discussion/forums/thread-view.asp?tid=129542

Somebody suggests that the gas (which expands the foam) leeches out over time reducing its ability to absorb impact. I think the conclusion of that thread, unsurprisingly, is that it's probably better to err on the side of caution.

Common sense suggests that many plastics / foams / rubbers do not last i.e. they become brittle / dried out over time. 10 years sounds reasonable and it's very likely that design, materials and technology will have evolved within that time to give a product that is at least more comfortable and pleasing to use if not one that offers increased protection.

In reply to ksjs: I guess, like harnesses, 5 years is a good age to looking at replacing helmets.
To me the gas leeching thing doesn't seem a relative problem. But UV degradation making the foam brittle would be more of an issue.