Another plastic that was critical to the war effort was "synthetic rubber", which was produced in a variety of forms.

Practical synthetic rubber grew out of studies published in 1930 written independently by Carothers and the German scientist Hermann Staudinger. These studies led in 1931 to one of the first successful synthetic rubbers, known as "neoprene". Neoprene is highly resistant to heat and chemicals such as oil and gasoline, and is used in fuel hoses and as an insulating material in machinery.

In 1935, German chemists synthesized the first of a series of synthetic rubbers known as "Buna rubbers". These were "copolymers", meaning that their polymers were made up from not one but two monomers, in alternating sequence. One such Buna rubber, known as "GR-S (Government Rubber Styrene)", is a copolymer of butadiene and styrene. It became the basis for US synthetic rubber production during World War II.

Worldwide natural rubber supplies were limited, and by mid-1942 most of the rubber-producing regions were under Japanese control. Military trucks needed rubber for tires, and rubber was used in almost every other war machine. The US government launched a major effort to ramp up synthetic rubber production, and by 1944 a total of 50 factories were manufacturing it, pouring out a volume of the material twice that of the world's natural rubber production before the beginning of the war.

After the war, natural rubber plantations no longer had a stranglehold on rubber supplies, particularly after chemists learned to synthesize isoprene. GR-S remains the primary synthetic rubber for the manufacture of tires.

Synthetic rubber would also play an important part in the space race and nuclear arms race. Solid-fuel rockets used during World War II used nitrocellulose explosives for propellants, but it was impractical and dangerous to make such rockets very big.

During the war, California Institute of Technology (CalTech) researchers came up with a new solid fuel, based on asphault fuel mixed with an oxidizer, such as potassium or ammonium percholorate, plus aluminum powder, which burns very hot. This new solid fuel burned more slowly and evenly than nitrocellulose explosives, and was much less dangerous to store and use, though it tended to flow slowly out of the rocket in storage and the rockets using it had to be stockpiled nose-down.

After the war, the CalTech researchers began to investigate the use of synthetic rubbers instead of asphault as the fuel in the mixture. By the mid-1950s, large missiles were being built using solid fuels based on synthetic rubber, mixed with ammonium perchlorate and high proportions of aluminum powder. Such solid fuels could be cast into large, uniform blocks that had no cracks or other defects that would cause nonuniform burning. Ultimately, most large military rockets and missiles would use solid fuels based on synthetic rubbers, and they would also play a significant part in the civilian space effort.