Microplastics expert David Jones of the UK's University of Portsmouth revealed that most modern chewing gum contains "a variety of oil-based synthetic rubbers," akin to the stuff that car tires are made of. As Jones explained, a chemical analysis revealed what Wrigley and other gum-makers would not: that sticks of chewing gum can contain everything from styrene-butadiene, which is what tires are made of; polyethylene, the chemical used for plastic bags; and polyvinyl acetate, which is better known as wood glue.