The process of treating rubber so it can be used to make things like car tires is vulcanization. Before vulcanization, rubber is soft and pliable. After this treatment, it becomes strong and hard.
The origin of the word vulcanization provides a clue about its meaning: it comes from Vulcan, the Roman god of fire. It won't surprise you to learn that the process of vulcanization involves extreme heat, in addition to the application of chemicals (usually sulphur). The technique was invented by Charles Goodyear, whose contributions were honored 40 years after his death, when the Goodyear Tire & Rubber Company was named after him.