Wonder no more. As you an see in the BMW clay model above it starts out with a rectangular metal frame that allows or varying wheelbases depending on the model being developed. From BMW adds a layer of wood and then a giant block or hard foam. That foam is then carved down to a rough shape of the car that is being designed (in this case a F30 3 Series). After that clay is added allowing designers to begin the final process of defining the details of the exterior design.
This final stage often sees several different final design concepts competing against each other with critiques happening in the BMW Design studio before going to the BMW board for final approval.
Why does BMW still work with clay when computers can easily replace this part of the process? Both former Head of BMW Group Design Chris Bangle and curren lead Adrian Van Hooydonk have been devout believers in the hands-on process of shaping a cars final design details by hand. According to both of them over the years, the process allows the designer to better understand the nuance of their decisions and form a fuller understanding of the shape they’re creating.