Originally Posted by rha600
I'd look at it in two ways.
1) seems kind of funny that only the makers of these helmets say to replace them every 3 years.
2) they are mostly stryofoam. the same stuff that environmentalists are complaining about because it lasts a billion years in garbage dumps.
show me some proof that this foam is breaking down in only 3 years (with out falls or other impact) that is put out by someone other than a helmet makers and I MIGHT believe it.
The helmets are made out of compressed EPS foam pellets, which means they are styrene beads expanded with air, then high-temp molded together under pressure. The beads will not break down, but the structure of the helmet gets tiny micro-cracks every time you put the helmet on and off, and the strains of everyday riding. These cracks reduce the ability to absorb impact. You can try this by gently squeezing coffee cup repeatedly.
Three years is likely a good rule for everyday users. 5 years is probably more practical.
Also, these designs tend to get better every three years anyway (stronger, more venting, lighter).