Plastic Injection Molding was a new plastic resin production technique that had just begun to gain traction by 1940. Dick converted the diecast company into a plastic injection molding company in 1941. Among the important products made were the first plastic squeeze bottles and an injection-molded proximity fuse case that was supplied to the US military in World War II.

Following the war, Dick renamed the company Rupert Manufacturing Company and relocated it to 1229 Montgall in Kansas City, Missouri, in 1947. Over the course of the following seventeen years, Rupert Manufacturing saw expansion due in part to the widespread use of injection molded products in the 1950s and early 1960s. Mr. Rupert spun off a few satellite companies during this period, including the Stratoliter.