Professor Philip Brainard, portrayed by Robin Williams, is an absent-minded scientist dedicated to creating a revolutionary energy source that could save Medfield College. Working alongside his robot assistant Weebo, voiced by Jodi Benson, he strives to impress his love interest, the college dean Dr. Sara Jean Reynolds, played by Marcia Gay Harden, who has already been let down by Philip’s repeated wedding day blunders. Despite his best intentions, he bungles their nuptials three times, leading to the accidental creation of Flubber, a bouncy substance that defies gravity and enables objects to soar through the air.
As fate would have it, after missing his third opportunity to marry Sara, he attempts to win her back with a Flubber demonstration. However, this goes awry when he tumbles out of a window, only stirring Sara’s frustration and causing her to begin a relationship with Wilson Croft, a rival professor played by Christopher McDonald. In a bid to redeem himself, Philip invents a flying car and devises a plan to use Flubber to enhance the Medfield basketball team's performance, which succeeds in securing a championship victory. Yet, his efforts do not rekindle the love of Sara.
In a heartfelt moment, Philip confides in Weebo about his feelings: she records him professing his love and later presents this revelation to Sara. This leads to an unexpected reunion where she kisses him, reigniting their connection. Meanwhile, the plot thickens as corrupt businessman Chester Hoenicker, played by Raymond J. Barry, seeks to exploit both Philip and his groundbreaking invention after hearing about Flubber from his inept associates Smith and Wesson, portrayed by Clancy Brown and Ted Levine.
As Smith and Wesson, in their greed, steal the Flubber and cause Weebo significant damage, Philip and Sara team up to recover it in an epic confrontation. Eventually, Flubber is cleverly utilized in a comical showdown to thwart Wilson's minions. The hilarious climax occurs when Wilson accidentally ingests Flubber, resulting in a chaotic yet amusing sequence where he uncontrollably dances and laughs due to the substance's effects on his system. The situation culminates in Wilson's over-the-top effort to expel Flubber, leading to a raucous exit that leaves everyone speechless and amused.
In the end, as they undergo a unique virtual wedding, Philip accidentally sets off one of his experiments, causing an explosion of hilarity. Following their unconventional vows, the newlywed couple takes to the skies in the flying car, joined by Flubber and Weebo’s newly created offspring, Weebette, symbolizing their love and zany adventures ahead.
