I knew that the bonnet and roof are made of aluminium and the bumpers are plastic, and I just assumed that the rest was steel. However, when I ran a magnetic GB sticker over the front wings and sills it didn't stick to these either. The only panels that it stuck to were the doors, rear wings and boot lid. By my reckoning that would make about half the body of the car either aluminium or plastic. I assume that BMW did this to save weight and it also means that stone chips won't rust, but will aluminium dent easier than steel? I've a nice "ding" on my bonnet which I think was courtesy of kids playing with a ball.