I need to replace the arm rest. How would I know if it is Nappa or just leather?

Nappa refers to the premium leather package on most Mercedes. From what I can see Mercedes only lists Nappa leather for this vehicle. It is most likely that there is no difference between the leather or Nappa listings other than price. I assume the listings that simply say leather are probably aftermarket, but will be just fine as an affordable solution since I see no seperate listing for a standard leather interior.