I thought this one had been solved...
It's Ford's soybean car, or more precisely: In 1941, Ford exhibited the “Soybean Car,” a lightweight plastic-bodied experimental vehicle, at the Dearborn Days community festival in Dearborn, Michigan, where Henry Ford’s company is headquartered.
"the frame, made of tubular steel, had 14 plastic panels attached to it. The car weighed 2000 lbs., 1000 lbs. lighter than a steel car. The exact ingredients of the plastic panels are unknown because no record of the formula exists today. One article claims that they were made from a chemical formula that, among many other ingredients, included soybeans, wheat, hemp, flax and ramie; while the man who was instrumental in creating the car, Lowell E. Overly, claims it was “…soybean fiber in a phenolic resin with formaldehyde used in the impregnation”"