[JesusFreke]

I'm honestly not convinced it's actually copper filled. The listing says it is, but its density says otherwise. Regardless, it was the most opaque thing I had on hand, so.. :)

There's some good info on opaque filament that people have found on this thingiverse object: https://www.thingiverse.com/thing:1662956. Personally, I've also had good luck with eSun's black PLA, although it was a fairly old roll, so who knows if their formulation is still the same. And their black PETG definitely isn't very opaque.

[bsdubernerd]

As I wrote before, I frequently go mostly with some gradation of grey nowdays. I keep a selection of fingernal varnish colors for finishing touches. They dry quick, cheap, are available in any shade you need in small volumes (so you can have variety over quantity). Especially the "gel" variants often require a single coat. I wonder if this could also work for shielding, just in case you're going to repeat the print :)