Originally Posted by
Lazyass
The 3-5 year rule is because of UV rays breaking down the foam and glue. That's the reasoning, anyway. Same in the motorcycle world. Those helmet manufacturers won't warranty a helmet past 5 years and stop selling replacement parts (padding, visors) for the old models. My current helmet was bought 5 years ago. I ordered a new Giro a few days ago simply because it was 50% off and I was ready for something new.
It's also because of the EPS construction. If you drop your helmet or it takes a hit, the foam will compress a little. When that happens, and enough times, the ability of the helmet to absorb impact becomes compromised. I believe most manufacturers will check the helmet for you.
J.