shredded A/C filter

Recently purchased 2720 that needed some cleaning up. Dropped grille off A/C and found pile of shredded white paper on the pan. The thin synthetic material filters were okay. Was that shredded paper also a filter or damper? Or perhaps it was simply carried in by the mice for their nest (yes, mouse evidence was abundant). If it is an integral part of the A/C, what is the part name or number please? The A/C is an RVP model 9000, I think.

Thanks, Krayfiver