A bumper is a vital safety feature on all vehicles and in order for a car to be considered roadworthy, it's a legal requirement to have both front and rear bumpers fitted.
The rear bumper reinforcer, is essentially a sturdy metal bar bolted on to the rear bumper, or onto subframe behind the rear bumper, which acts as a bolster to the bumper, providing extra protection, and supporting the role of the bumper in the event of a rear end collision.
The job of the rear bumper is to absorb the impact of a crash, therefore offering protection to the car, by minimising damage to the frame and body of the car as well as internal and external parts. The rear bumper also serves to protect the occupants of the car in the event of a crash. By absorbing some of the impact of the collision, the rear bumper minimises the force of the crash for driver and passengers. The rear bumper is fixed to a bumper bracket on the rear of the car, enabling it to absorb some of the impact from a rear-end collision. The bumper rear reinforcer is fixed onto the rear bumper, or behind it on the subframe, and functions to assist the rear bumper, adding extra reinforcement.
If the bumper rear reinforcer needs replacing, having suffered damage in an accident, for example, it's advisable to buy a new or replacement part that has been manufactured to fit the make, model and year of car.