At least lead, or maybe even depleted uranium. Who knows, even gold could qualify as ballast. But ballast has to posess a very high amount of mass to volume. You want to be able to position the ballast in some of the weirdest locations, and it has to be small.
I'm pleased with the look of the new BMW, but concerned about the front suspension fairings (where they join the carbon fiber arms to the chassis). The fairings appear very large and definitely affect airflow.
Racing should be decided on the track, not the court room.