Acetal Copolymer is the new material I have been using to produce shift knobs. Its a very hard plastic which was invented by DuPont as the lightweight replacement for steel. It is strong, durable, somewhat scratch/dent resistent and has great heat characteristics. It wont get hot or cold like metal ones, it remains within a moderate temperature range similar to your steering wheel.
Its lighter, but this only aids in providing more feedback to the driver. I noticed a better connection with the shifting using one of these over aluminum ones. Perhaps being lighter it doesn't damped the feedback like the heavier metal knobs do.
All in all, its a great material and its proving to be loved by each person that gets one.
WC LATHE WERKS