I think if you were to consult with a helmet expert you would find that the useful life recommendations aren't based on the outer shell material, but rather on the expanded rigid foam material on the inside that provides the actual shock absorption. It's a more complex material than the simple "Styrofoam" in a cheap ice chest, but it still degrades over time just like that Styrofoam ice chest. And that rigid foam is the reason the helmet manufacturer's do not endorse painting a finished helmet. Solvents degrade the foam rapidly. Dump a little lacquer thinner or gasoline on your ice chest and see what happens.
The outer shells can also degrade over time, but that is more likely to affect penetration standards rather than the impact standards.
Jerry
Iwas thinking of painting the styrofoam on the inside Jerry.
spyder
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Topic: Helmet Vents (Read 4291 times)