You know the feeling-you have taken the occasional rock or ice chunk to the head or had a couple of nasty falls on your mountain bike but don't want to get a new helmet without knowing for sure the old one is toast. Well now you will be able to know for certain if it is necessary to replace your helmet with a new process that causes stinky oils to seep out of plastic materials when they are damaged.
Only completely damage-free helmets do the job of protecting your head properly. Normally it is recommended that you buy a new helmet after a certain period of time but it is hard to throw away a perfectly good helmet and spend money on a new one.
Developed by research scientists at the Fraunhofer Institute in Germany, a new helmet making process produces polymer materials or plastics that start to smell if they develop small cracks. Large cracks will really cause a stink.
The smell comes from stinky oils enclosed in microcapsules, measuring just 1 to 50 micrometers, which break if cracked. A layer of melamine formaldehyde resin encloses the capsules so that they are completely airtight and mechanically sealed until broken.
The capsules will open and exude the stinky substance at a level according to the amount of damage, as a sort of warning indicator. This means you will know you need to change out your helmet way before the damage gets outside of the recommended safety range for failing.
For a bike helmet, the microcapsules are inserted in a thick foil made of polypropylene, which is fastened to the head gear. So now you know if you are intentionally dropped on your morning ride or can't find a belay partner anymore, it is probably time for a new helmet.