At 5GHz the skin depth is pretty shallow; in units(1), sqrt(2 / copperconductivity 2 pi 5 GHz mu0) says 0.93 microns. I think you could probably get by with 3 microns of copper vacuum-deposited on Mylar or on fiberglass window screen.
Steel window screen coated in copper might work even better and could be made by electroplating first a nickel flash and then the copper layer, avoiding the expense of vacuum coating. I'm not clear enough on the physics to be sure, and maybe it would be worse, but the skin depth in even ordinary steel is about an order of magnitude smaller because of its magnetic permeability.
"Booster bags" for shoplifting use (ungrounded!) aluminum foil. I think the reason they have to be several layers thick is that anti-shoplifting RFID tags operate at a much lower frequency, and aluminum foil is typically only 10 microns thick.
Steel window screen coated in copper might work even better and could be made by electroplating first a nickel flash and then the copper layer, avoiding the expense of vacuum coating. I'm not clear enough on the physics to be sure, and maybe it would be worse, but the skin depth in even ordinary steel is about an order of magnitude smaller because of its magnetic permeability.
"Booster bags" for shoplifting use (ungrounded!) aluminum foil. I think the reason they have to be several layers thick is that anti-shoplifting RFID tags operate at a much lower frequency, and aluminum foil is typically only 10 microns thick.