Polypropylene is used in many of the bumpers on import and domestic cars. The plastic is usually black and sometimes gray. Polypropylene has a waxy feel to it and it smears and gets "hairy" when sanded at high speed. If you have determined that the plastic you are going to weld is polypropylene, this is the plastic welding rod you need. Use this plastic welding rod with either Polyvance's airless plastic welder or a hot air plastic welder. No pigment has added when we make this rod. This package contains 30 ft (9.1 m) of polypropylene plastic welding rods. Each rod measures 12 in (30 cm) long.