Car tires are generally considered environmentally unfriendly because they are predominantly made from fossil fuels. Natural rubber is generally not used anymore; most tires are made from isoprene, which is chemically very like rubber but is produced by thermally breaking apart molecules in petroleum in a process called cracking. The isoprene is separated out and purified and then reacted to form the artificial rubber that is the major component in car tires. The tires eventually end up discarded in giant piles that represent one of our biggest waste disposal problems.
