Copied this from Arai support ... was told same for all lids when doing my DAS / CBT
Hope it clarify's thing for you looniebiker
Perhaps the ultimate demonstration of a company's faith in its product is how strongly it is willing to warranty it.
For nine years, Arai was the only helmet company we know of that offered a warranty longer than one year. Arai's was, and is, a full 5-year warranty.
But even a helmet as good as an Arai won't last forever.
Like most major helmet manufacturers, Arai subscribes to the Snell Memorial Foundation benchmark of five years as the suggested usable lifespan of a motorcycle helmet. Why? Think of a helmet in terms of your body. No matter how good it may look, or how well you take care of it, age still takes its toll. Even with minimal use, a helmet is affected by things like the acids and oils in sweat, haircare products, pollution, exposure to UV rays, etc. At about the five-year mark, helmet interiors begin to show wear and/or deterioration, which should serve as an alert to its overall condition. The helmet's fit may begin to feel a little "loose", not as snug as it once did. This unseen aging and deterioration of the EPS liner and fiberglass shell can affect the helmet's ability to perform in an impact as it was originally designed. If a helmet suffers an impact and any doubt exists as to its further ability to protect, it should either be returned to the manufacturer for competent inspection or discarded and replaced.
These are the reasons to replace your helmet after five years. Of course, if your helmet becomes less than snug in fit, or damaged, it should be replaced before the five year mark. And when you do, you may want to remember that Arai was the first company willing to warranty its helmets for the full Snell-recommended usable lifespan.