Some of the features of a super-efficient hypercar include use of lightweight composite plastics. They are as strong as steels, but in place of steel bodies can provide comparable crashworthiness, and reduce the car's mass by several-fold. Mass is the single largest factor that prevents high fuel efficiency. Composite plastics hold the potential for shaping a roomy, comfortable car with 50 to 75 percent less mass. Composites allow for superior aerodynamic streamlining that makes cars slippery, reducing air friction that causes efficiency losses.
Lighter cars allow for lighter structural parts, achieving further reductions in mass.
The aircraft industry pioneered the use of composites, as in this unmanned air vehicle designed by AeroVironment. Image courtesy of Dale.