The essential part of the helmet for impact protection is a thick layer of firm polystyrene, plastic foam, that crushes on impact, absorbing the force of the blow. All helmets require a chin strap to keep them in place in a crash.
Hard-shell helmets also have a hard outer shell of plastic or fiberglass that provides a shield against penetration by sharp objects and holds the polystyrene together if it cracks in a fall or crash. These helmets are more sturdy but tend to be heavier and warmer than the soft-shell models.
Soft-shell helmets have no hard outer shell but are made of an extra-thick layer of polystyrene covered with a cloth cover or surface coating. The cloth cover is an essential part of many soft-shell helmets. If the helmet comes with a cover, the cover must always be worn to hold the helmet together if the polystyrene cracks on impact.
Both types of helmets meet CPSC standards; the main difference is style and comfort. The soft-shell helmets are lighter than the hard shell versions but may be less durable.
Although there is no consensus on the relative safety of the 2 types, models of both types have passed the CPSC test. The soft-shell helmets are lighter than the hard-shell versions but may be less durable.
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