I'm having a hard time getting Karma to render these bee wings correctly. The best I can do is use a reverse node back in /obj to switch which side is transparent, but I can't figure out how to get both to be. The geo itself has no depth, just a flat plane. Thanks in advance for any tips!

I seem to have found a semi-solution: the "classic" shader works. Still, seems like principled should be able to do this, no?

Hi. Direct refractions for light sources that are facing geometry normals are disabled by default for performance reasons, so you can run into this issue for refractions on non-manifold/non-closed geometry. You can use Render Geometry Settings LOP and set "Direct Refractions Subset" parameter from "Outside" to "Both" have the refractions evaluate on both sides.
BTW principled shader does not support thin film refractions, so refractions won't look correct for flat single-sided planes like this. I would recommend using the Classic shader instead which has the thin film refraction toggle.

dlee
Hi. Direct refractions for light sources that are facing geometry normals are disabled by default for performance reasons, so you can run into this issue for refractions on non-manifold/non-closed geometry. You can use Render Geometry Settings LOP and set "Direct Refractions Subset" parameter from "Outside" to "Both" have the refractions evaluate on both sides.
BTW principled shader does not support thin film refractions, so refractions won't look correct for flat single-sided planes like this. I would recommend using the Classic shader instead which has the thin film refraction toggle.

Great, thanks for the info! I'll stick with classic here.