Where does a car tyre come from, and where does the worn-off rubber go?

In numbers

• 1844vulcanisation was patented
• 1888the first practical pneumatic tyre

In five stops

1. 1

   Where were its atoms born?

   Rubber's carbon and hydrogen come, like those of other living materials, from the Big Bang and from stars. The sulfur that toughens the rubber and the iron in the tyre's steel wires formed in massive stars and stellar explosions.

2. 2

   How did nature prepare it?

   Natural rubber comes from the milky sap, or latex, that flows when the bark of the Amazonian rubber tree (Hevea brasiliensis) is cut; it is a long chain of small molecules called isoprene. The carbon in synthetic rubber and carbon black comes the same way as gasoline's and plastic's: from oil.

3. 3

   What did people do?

   Raw rubber turns sticky in the heat. In 1839 Charles Goodyear noticed that rubber heated with sulfur stayed firm and springy; he patented this process, vulcanisation, in 1844. The first patent for a pneumatic tyre was filed in 1847, and John Boyd Dunlop made the first practical one in 1888. Today the rubber mix is cured in a mould together with layers of steel and fabric.

4. 4

   What happens when we use it?

   A tyre grips the road by rubbing against it, and tiny pieces break off with every kilometre. That's why the tread wears down over the years: the rubber hasn't vanished, it has been left on the road.

5. 5

   Where does it go next?

   Worn tyre particles are washed by rain into streams and seas and are counted among the sources of microplastics. Tyres at the end of their life can be retreaded, ground into products such as sports-field surfaces, or burned as fuel, mostly in cement plants.