The bug

The inside faces of the newly-implemented copper grate blocks do not render. As MC-169969 is currently triaged, I do not believe that the current copper grate behaviour is expected.

Expected results

The back faces would be visible from all angles.

Actual results

They are not.

How to fix

I have attached to this issue a resource pack that fixes this completely, as well as MC-169969, through a simple set of template models. All four copper grate oxidation states, spawners, and powder snow are pointed at these new template models to make sure they render hollow as expected.

I give full permission to Mojang to include these assets in future releases of Java Edition as to fix this issue.