Poster board painted with "Liquitex" varnish and dried in fume hood 3 hours. Lightly brush on a small amount of mineral oil and then apply well mixed epoxy resin. Pour fine -mesh activated carbon/ graphite on both sides over a pan. Lightly press. leave 24 hrs. Aplpy a six-ton press. Light mass/ wide surface area. Not flexible but there are applications like "air batteries". We will see....
Note: I did not like the measured resistance I observed for this approach. It looks nice , but not useful.
However: try deforming styrofoam cups in ethyl acetate solvent. It forms a viscous paste and you can dilute it as needed. I added graphite and finely screened activated carbon. Apply with brush to surfaces including poster board. Let dry 24 hrs. Resistance varies but does conduct! Is it copper? No, but has potential use. Experiment with the application of the paste. I saw some low ranges of 200k ohm with a multi-meter at varying electrode distances. Much safer than using acetone , in my opinion.