Originally Posted by
Notso_fastLane
The thin plastic is only really there for 1) decoration, and 2) protection from sun/UV damage that can degrade the polystyrene. My first bicycle helmet was just the polystyrene, with a changeable, washable, cloth cover.
Originally Posted by
zeppinger
This is not true. The thin plastic shell on a bicycle helmet is designed to spread out the impact of a small dense object, like a curb, onto a wider area of foam. This is a major criticism of bicycle helmet design because the plastic is sooooo thin it is unlikely that much spreading is going on. In motorcycle helmets the plastic shell is quite thick and far more effective.
Both are not true. Although the UV protection would be a side benefit.
Bell made the first US bicycle helmets and they had a very hard shell on them (white helmet with red strips).
Then after many years, helmet manufacturers started making the polystyrene with changeable, washable, cloth covers. Partly to make them lighter but mostly because they were cheaper to manufacture.
Helmet manufacturers quickly learned that the polystyrene with cloth cover helmets caused significantly greater rotational brain injuries and neck injuries, due to the uncoated polystyrene holding to the concrete/asphalt when the helmet hit the ground with the rider still moving laterally. Helmet manufacturers then had a problem where their helmets were causing injuries.
To fix this huge liability problem, helmet manufacturers put the thin plastic coating on so the helmet would skid along the ground rather than catching. And to get rid of the evidence, helmet manufacturers offered free helmet exchanges of a new helmet for your old helmet that had been in an accident. Helmet manufacturers never notified the public of the danger and never did a costly recall.