UV definitely destroys the (break-resistant) properties of Polycarbonate (i.e. GE's Lexan®) products. If you were to leave the helmet exposed to direct daylight everyday, it would be practically worthless as impact protection within 3 yrs....however, for me I ride less than 24 hours/week and I don't have any problem with trusting it for a 5 year period....providing I don't do any 'yard-dart dismounts'. I'm afraid that Giro has become a Brand that I 'used' to use, now that their helmet prices approach the $200 mark ....I'm sure that next year's helmet will be >$220......I've started using the MET helmets which I like as-well/better and are much less expensive.Henry Chinaski said:http://www.bhsi.org/replace.htm
UV can affect the strength of the shell material, though. Manufacturers put UV inhibitors in the plastic for their shells that control UV degradation. If your helmet is fading, maybe the UV inhibitors are failing, so you might consider replacing it. Chances are it has seen an awful lot of sun to have that happen. Otherwise, try another brand next time and let us know what brand faded on you.
In sum, we don't find the case for replacing a helmet that meets the ASTM or Snell standards that compelling if the helmet is still in good shape and fits you well. "