Soapbox car were first produced by the end of ‘800 with the same design as the first real motor cars. Firstly, craftsmen made them only with wood pieces. In the ’60, cars were produced on industrial scale with metal components.
Since demand for soapbox cars skyrockets, production shifted to Moplen and plastic for the components for economic and practical reasons. Soapbox cars became a mass product thanks to the fall in price.