Hard plastic that breaks easily and is difficult to replace on a 300RR. The second one broke in less than a year. In 25 yrs of riding I have never bent or broken an aluminum subframe. What's more all the wiring for the RR, the battery box, air box, lighting etc. is integrated so it takes 2 hours of painstaking work to remove and install a new one. Sorry Beta but this really is the worst thing about the bike.