It's reasonably hard plastic. My scissors went right through it like butter though when I gave it enough leverage (by putting one blade through one hole, and the other through one fairly far away). The only risk doing it with scissors is slipping and cutting the wire, but I managed to avoid doing that. Honestly the hardest part of the entire mod is removing the outer black plastic mesh (I couldn't get the leverage if I didn't remove it). Those little tabs, especially the glued ones, are tricky. On the cup where the cord comes in, it is even more difficult, because there is a glued tab right next to the exposed end of the cord (where it connects to a circuit board).
I think we can file this mod under "unessential and for aesthetic purposes with no detriment to sound, though no proven improvement". Obviously I can't A/B a modded pair with an unmodded pair at this point, but any improvement in soundstage seems to be minimal. The sound certainly didn't get worse, but it wasn't as big of a change as doing the foam mod was (where I could immediately tell that the lower frequencies were suddenly present where they hadn't been before).
In other words, I'd highly recommend the foam mod, and I'd only recommend this particular mod to someone seeking either that last .05% performance out of their headphones, or improved aesthetics.
Sorry if my comments were misconstrued as "the white paper is inessential". I was actually asking whether or not it was. I googled and found out that it is likely essential, so I ultimately left it in.