Why is the rubber tip of my capacitive stylus no longer conductive?

In 2014, so eight years ago, I bought five styluses from China. Cheap stuff obviously. They worked fine while I used them, but soon after they were just left in a drawer. Last night I realized that they all don't work anymore. I cant even make a single click on my phone. I also tried with other devices.


The pen, all of it except for the rubber tip, is made from stainless steel.


The tip is made like a small bladder from black rubber. When you press it against a surface, from any angle, it presses against that surface with an are similar to a circle with a 5mm diameter.


The rubber does not appear to be cracked, deteriorated, discolored or anything like that.


From what I can read, the rubber tip is most likely made from so called conductive polymers. Is it normal that these age / deteriorate in such a way, that they lose their conductivity?


My friend suggested, that if it was some kind of conductive carbon / graphite, that might simply "fall of" the rubber as dust.


I am asking out of simple curiosity :)


