How long do motorcycle helmets last? Five to Ten years or longer.
Dissertation from a plastics engineer (me) follows...
The principal enemies of your helmet are:
1) Impacts - not just dropping it on the ground, other than repeated
drops - if your helmet cracks or breaks because it fell off of your seat
in a parking lot, do you think it was that good to begin with?
2) UV degradation (sunlight)
3) Chemical attack (gasoline, solvents, etc.)
Using your helmet will reduce its protection capability over time. A
fairly long time: 5-10 years. Your head gives off chemicals (sorry guys
and gals) that will attack the inside of the helmet.
As far as what they are made out of, that information is readily
available from various sources. They are not much different now than
they were 10 or even 20 years ago. (Kevlar and Carbon Fiber composites
come to mind for the newest and most expensive ones). Newer ones are
definitely better, due to improvements in design, testing, and materials.
Almost all helmets still use expanded polystyrene foam underneath the
pretty exterior, and modern processes use inert gases to create the
foam, so that part doesn't self-destruct on its own, either.
If you bought a new helmet in 1994 and put it in your closet, left it
there for 10 years, then finally took it out and started using it, then
it is as good as it was back then. The materials that they are made from
take a very long time to degrade due to normal environmental elements in
your house. 10, 20, 50 years. Possibly more.
Store it in the dark, in a vacuum, at a constant 70 F, and I say the
helmet would still be the same 100 years later. Beyond that, who cares?
I have a 1997 Shoei RF-R that I bought "new" 2 years ago, and to me,
it's a 2-year old helmet. I have no fear of it being "old" when I am
wearing it. I actually own several RF-R's because I was given a whole
bunch of shields for free from the USA Company who makes them for Shoei
(it used to be me who made them, for earlier models).
Despite the above, I like the fit and feel of HJC and KBC helmets
better. But I digress...
Your helmet is good for at least 5 years of use, unless you crash with
it, spill some solvent in or on it that attacks it, wash it a lot
(cleaners are solvents), or you leave it outside in the sunshine for a
year or more. Or, you never take it off of your head.
You will usually see things that are indicators that it's time to
replace your helmet. On the outside, dings from many bumps or drops. On
the inside, worn padding or foam falling out. If you take reasonably
good care of your helmet, the first thing you'll notice is worn straps,
worn pads that touch your head, and the foam immediately underneath
changes consistency.
If your helmet is 10 years old and still looks good inside and out, it s
probably still a good helmet.
I have a 1975 Shoei S-12 Full-Face helmet. Although I don't wear it, if
given the choice between that and no helmet at all, I would wear it. (I
am guilty of occasional short rides with no helmet)
Whatever helmet you have, wear it. Wear it out. Then get another one.
-Fig