would have to be paper thin.. but im not sure tk has any sort of actuall rubber in there id think it was all just glue based rubber stuff
I have seen a few Keeley bro laminates with rubber inserts and yes the cut off was only a quarter of the face but it hate a rubber type sheet in there
I've got some regupol which is acoustic matting made from cork and rubber but I think it's a little thick. I'll make some enquiries and find a thinner alternative.