A college professor invents an anti-gravity substance which a corrupt businessman wants for himself.
When Professor Brainard experiments further on Flubber derivatives, he gets in trouble and only his students can help.
Professor Philip Brainard (Robin Williams), of Medfield College, is developing a new energy source in an attempt to raise enough money to save the college from closure. His preoccupancy with his research distracts him from his fiancée and the college president Sara Jean Reynolds (Marcia Gay Harden); he has missed two weddings in the past as a result of this, much to the anger of Sara. On the day of the third attempted wedding, Philip is approached by his former partner Wilson Croft (Christopher McDonald), who has profited from ideas he has stolen from the chemist and now desires to steal Sara from Philip and make her his wife, which he declares directly to Philip, though Philip takes it as a joke. Before he can make it to the wedding, his latest experiment shows fast development, forcing him to miss another wedding. The resulting substance created from the experiment is a living green goo that increases in speed as it bounces and proves to be difficult to control, wreaking havoc on the neighborhood before the professor finally manages to capture it. Weebo (voiced by Jodi Benson), Philip's hovering robot assistant, classifies the substance as "flying rubber", leading Philip to christen it as "Flubber".