• PP, PPO, TPE, TEO or TPO (thermoplastics) – These plastics make up about 80% of bumpers because they’re better suited to large volume runs. The excess that results from the molding process can be recycled back which makes them environmentally friendly and cost-efficient. But the molding process also introduces a small percentage of wax-based mold release into the plastic which repels paint and adhesives so the surface requires an extra step while prepping. The surface smears and melts easily with high-speed grinders and sanders and gets stringy when hot so you may have to let the repair area cool from time to time while sanding.