Chewing gum is a type of gum traditionally made of chicle, a natural latex product, or synthetic rubber known as polyisobutylene, which is a non-vulcanisable form of the butyl rubber (isoprene-isobutylene) used for inner tubes or to line tubeless tires. For reasons of economy and quality, many modern chewing gums use rubber instead of chicle. Chicle is nonetheless still the base of choice for some regional markets, such as in Japan.