Originally Posted by
bpcyclist
That is so interesting, thank you. So, but, that would suggest if I live in San Diego or Barcelona that my time frame for helmet replacement should be quite a bit different than if I live in Manchester or Seattle, right? Do you think the bike shops in sunnier climates know this?
No, the degradation due to UV is limited to the upper layer and has almost no significance to the mechanical strength.
And even that won't occur unless you remove the plastic cover and scrape off the protective surface film.