Passenger side floor board

This Z has a poly-fiber type covering on the lower areas on both passenger and drivers sides floor boards. I don't know if this was something that was done after a floor board repair or ? I've never seen this before. The floor boards look great in this Z, no rust or anything that looks like a repair was made. If anyone seeing this can let me know what I have here, please let me know. I hate to admit that I have owned this Z for 7 yrs and I'm just now seeing this. I was told by the previous owner that this Z is free from rust and I took a quick look at the problem areas we all know about, and seen nothing that worried me. This Z was (and still is) in such great condition when I bought it that I couldn't imagine it having rust issues, and it hasn't. I can say with complete confidence that I have not seen any areas of rust on this car.