We’ve all been there –hastily putting the car in reverse, failing to check the blind spot, and cringing at the crunch of bumper meeting barricade. The resulting dents used to mean a quick trip to the auto parts store for some cheap body filler and a can of spray paint, but plastic bumper parts require an entirely different arsenal of products. Instead of the old sheetmetal bumper exteriors, modern cars hide the metal bumper under a plastic fascia in hopes that minor abrasions might pop out more easily. But if your car meets the sharp edge of a 2-foot parking barrier, the semi-flexible plastic can easily rip, bend, or break.
Text taken from http://www.instructables.com/id/Plastic-Bumper-Repair/