The mesh looking inserts on the lower part of the bumper/ front spoiler? I use Griots spray on car wash (lubricant that adds gloss and some wax protection). I scrub it with a light touch horse hair brush. After that if you want..add a interior protectant wipe (I use griots) It's like a dressing that can also be used on tires...
1988 325i sedan (Cirrus Blue Metallic, Silver Grey Leather)
2011 128i convertible (Blue Water Metallic, Grey Leather)