There are reinforcing fibers that automotive tire manufacturers advertise made of steel and kevlar for higher performance tires. Kevlar is plastic and IIRC was

There are reinforcing fibers that automotive tire manufacturers advertise made of steel and kevlar for higher performance tires. Kevlar is plastic and IIRC was invented in the 60's. From riding a bicycle as a hobby, most of my puncture flats on the road come from tiny steel strands that come off of tires that have been used a little too much. I imagine the steel fibers just rust away eventually but the kevlar just gets ground into tinier and tinier bits.