According to Alan Belcher "Bisping has a Plastic chin".

Speaking via his Yahoo Sports blog Belcher put:
“He never fights confident, he fights defensive, which is why he’s hard to hit. He’s still fast, very technical, with great cardio and some good skills. He’s not easy to hit clean, which is why he’s only got KO’d twice despite having a plastic chin. But I am prepared. I know the guy better than he knows himself right now. I have more power than you. I can walk through your best shots and keep on coming at you. Bisping, you panic when you are put under pressure, when you get clipped, and that panic is going to get to you again on April 27. You don’t want to be panicking in the Octagon when you are locked in there with a finisher like me. I can submit you and I sure as hell can turn your lights out just that – boom! I have no doubt in my mind that Bisping cannot hurt me. I have no doubt that even if I let him hit me in my face, the worst he could do is cut me. He can’t stun me, can’t do nothing.”