Are plastic bumpers good?
Plastic is also considered to be safer than metal as a bumper material since plastic does a better job of absorbing an impact during an accident. This is because plastic is meant to crumple and dent during an accident rather than hold its shape. via
Is the bumper part of the frame?
The bumper you have off is just a cover for your real bumper which is what you are describing. That bumper, the real one, is tied to your frame and is actually absorbing the energy from impact where the facade is just existing as a cover due to the ugliness of the actual bumper. via