Pretty sure it's the egg crate lighting panel diffuser material, judging by the untampered with stuff up in the corner of the pic.
The matial filling the grids could be something as simple as plaster of Paris, and then just hit with some tan paint.
What I'll probably do is secure it down to some sort of plaque / mount, hotglue around the outer edges, and then pour two part expanding foam into the grids and sand like I speculated they might have down on the original. Then hit it with a little tan paint, again like I speculated they might have done, and I'll have a nice little Cantina themed plaque to display my Evan / Ponda Baba shared blaster.