Cracked cycle helmets cause a stink

Cyclists and skiers know they have to replace their helmets if they drop them. Now polymer materials can be produced which start to smell if they develop small cracks. The larger the crack, the stronger the stink, according to this article on sciencecentric.com. The smell is released when tiny capsules in the plastic break.

Apparently the microcapsules are inserted in a thick foil made of polypropylene and enclosed by a layer of melamine formaldehyde. Watch out for bikers and skiers sniffing their helmets.