A number of used motorcycle helmets have appeared in the Classifieds section.
You should never, ever buy and use a second-hand helmet! It's very dangerous.
Helmet materials degrade over time and even a small impact (e.g. a drop from 1.5 metres) can compress the protective elements of the helmet rendering it ineffective if you are involved in a collision. There are no visible, external signs of this kind of degradation, so you have no way of knowing if that cheap helmet will save you or kill you.
If you are tempted by a new or "never used" helmet from a private seller you must check the date of manufacture (the date of original purchase is irrelevant) as helmet manufacturers do not recommend using a helmet older than 5 years, even if it hasn't been used.
End of pompous lecture.



