My friend has recently purchased a new bike. The guy who sold it to him was clearly giving up the sport, so he gave to said friend his helmet as well (MET parachute for MTB).

As my friend already had a functioning helmet, he is now trying to sell the second one (within our rough group of people with whom we ride primarily). Now I personally believe it is just morally wrong to do this as he cannot know what the helmet has lived through, although it appears to be free of dents and has few scratches.

So am I being silly or is it just wrong to sell a second hand bicycle helmet?

Note: He sells the helmet he was given with the bike.

  • 1
    Could you please edit the question to make it unambiguous.As written, you friend is trying to sell his helmet. Which helmet he is selling.
    – mattnz
    Commented Sep 10, 2018 at 22:14
  • 3
    Possibly belongs over on Interpersonal Skills Stack Exchange.
    – mattnz
    Commented Sep 11, 2018 at 2:38
  • 4
    This is an ethics question, not a bike question.
    – Adam Rice
    Commented Sep 11, 2018 at 2:46
  • 1
    @mattnz I read it to be the helmet of unknown history, which raises the ethical question.
    – Criggie
    Commented Sep 11, 2018 at 3:17
  • 1
    You wouldn't buy a second hand toothbrush, shoes or underwear!
    – Carel
    Commented Sep 11, 2018 at 7:14

2 Answers 2


I personally would not sell or give away a bike helmet that is not brand new, kept in its packaging or is guaranteed to be unused and undamaged.

Bike helmets protect the head in a collision by absorbing energy and breaking down. Any prior damage takes away from the ability to absorb energy. It's impossible to truly know what damage a used helmet has sustained, therefore, you should not use such a helmet yourself nor pass on a helmet on to anyone else because you have no idea how it will perform in a crash. Yes, you can inspect the helmet for marks on the shell that would indicate if the helmet has taken any impacts, but it's not reliable enough, IMHO.

However, if your friend fully discloses how he got the helmet and that its history is unknown then he is acting ethically, because your friends can decide to take the risk or not.

  • 3
    Is there any scientific data on how well a helmet still performs after minor use? I’d be very interested in a comparison with different ages, UV exposure and usage. How much can you actually damage a helmet without it being visible?
    – Michael
    Commented Sep 11, 2018 at 10:59
  • There is a link in the answer here. bicycles.stackexchange.com/questions/46302/…
    – mattnz
    Commented Sep 12, 2018 at 23:28

There's no evidence that used, but uncrashed helmets are any more dangerous than new. In this study:

"Foam cores were extracted from 63 used and unused bicycle helmets"

"Based on these data, the impact attenuation properties of EPS foam in field-used bicycle helmets do not degrade with the age."

"Based on these data, old helmets should not be discarded based on an incorrect assumption that their impact performance has deteriorated with time."

The only variable that was "impactful" was the density of the foam.

Source: https://asmedigitalcollection.asme.org/biomechanical/article/138/4/041005/371203/Age-Does-Not-Affect-the-Material-Properties-of

Furthermore, per hour of commuting, you are actually more likely to get a TBI riding in a car vs biking, 0.41 vs 0.46 per million hours traveled. I have yet to see anyone wear a helmet in a car, which makes me think that most people are worried about bike helmets for cultural reasons rather than doing an honest risk assessment.

This study goes on to make the stunning conclusion that:

The benefits of cycling, even without a helmet, have been estimated to outweigh the hazards by a factor of 20 to 1 ... Consequently, a helmet law, whose most notable effect was to reduce cycling, may have generated a net loss of health benefits to the nation. Despite the risk of dying from head injury per hour being similar for unhelmeted cyclists and motor vehicle occupants, cyclists alone have been required to wear head protection.

Source: https://www.sciencedirect.com/science/article/pii/0001457596000164%20

  • I think the reason people don't wear helmets in a car is because in a car they rely instead on seat belts, air bags, crumple zones, etc etc. Commented Aug 18, 2021 at 5:02

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