Richard Kim, who designed the exteriors of both vehicles says:
The carbon fiber in the i3 city car and i8 sports car significantly reduces the weight of the vehicle and the size of its frame, giving designers more flexibility and creating more interior space for passengers
The doors of the car are mostly made of glass. BMW said the car offers “superb safety in the event of a collision.”
The all-electric version, i3, can go 80 to 100 miles on a single charge. It also comes with option of adding a small gas engine. It takes about six hours to fully charge the battery. The four-door i3 is designed for urban driving. Where the sporty i8 has two winged doors made of glass and a sleek silhouette. The all-wheel drive car has a battery and a gas engine that work together.
Source: yahoo news