Carbon composites are plastics with carbon fibers mixed in, for reinforcement. The resulting material is quite strong while being 50% lighter than steel and 30% lighter than aluminum, which is why planes, such as the Boeing 787 Dreamliner and Airbus A350, use it. Now the composites may be coming down to our cars. The reduction in weight should drive the composite vehicles to new efficiencies, but there is a catch, of course. Carbon composites are not cheap and may add $5,000, or more, to the cost of the vehicle.