See this thread on sound deadening. It has my photos, and many others. https://www.clublexus.com/forums/rx-...this-rx-4.html

 

As some have already mentioned, it's felt-lined for sound deadening of road/tire noise and noise from rocks/debris picked up by the tires and hitting the wheel well. Cleaning with a hose worked well and in rare cases, power washing for stubborn stains/dirt. No issues through the Canadian winters - very durable.

My Gen 2 IS had the same felt-like material and was disappointed to see the new IS moved to a "cheaper" rubberized/asphalt coated plastic wheel well. The NX has the same material as the new IS. Wish they both came with the felt-material as it looks richer and absorbs debris sound better.

 

It sure don't help keeping "road" noise out of the cabin.............