Many people think that plastic is not strong enough to break easily. It would be nice if it was replaced with metal. But this is done for security reasons. Because if it hits a pedestrian, plastic is safer than steel. Although there maybe no difference when the speed is too fast. But plastics can greatly reduce the risk. And plastic is generally lighter.Installing this material can reduce the quality of the vehicle. And there are still many cars with all-aluminum bodies. On the one hand, it is to reduce the mass of the car, on the other hand, it is to absorb the energy of the collision.