The Plastics Inventor (1944)

Donald is listening to a radio program that tells how to build an airplane from plastic, in a process much like baking a cake, cookies, and making toast. He takes it out for a test flight, still guided by the radio, and it works wonderfully. Until the radio interviewer asks if there's any problems: yes, it melts when it gets wet. Of course, Donald instantly flies into a rain cloud, and has to battle his plane as it disintegrates.