Backing Plate Gaskets?

I looks like there was a factory paper gasket behind the front backing plates (10" drum) on this '65 Valiant which ripped up when removing the plate. Does anyone know the intended purpose of placing a gasket in this location? I don't see anything there that needed "sealing". Thank you.

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Actually it's thin foam. Almost the same as in a TV wellbox. I usually take that and it works great.