Hi there,
check out my screenshots down below.
In Eevee: I am having an object with a partly transparent material (Principled BSDF, Alpha <1). In the Material Properties Tab > Settings > Blend Mode ist set to Alpha Blend, “Show Backface” is disabled. Everything looks like desired, the backface is not showing trough the transparent mesh.
In Cycles I can’t make that hapen, the backface is always shining trough. no matter if “Show Backface” is unticked. The “Show Backface” option in Cycles is located under Material Properties Tab > Viewport Display.
Any Ideas why that is and how to fix it? Am I doing something wrong?
Thanks everybody
Cycles is tracing actual rays, so the Alpha Blend and Backface options, which are Eevee settings, don’t affect it. That’s why they move to Viewport Display when you switch to Cycles, that’s the devs trying to convey that those settings are now only relevant in Material Preview.
If you want to do the same in Cycles, you’ll have to set up a few simple nodes. The most direct analogue would probably be using the Backfacing input to switch the material to a Transparent, but you’ll notice that doesn’t fully solve the problem in this case, since any transparent front faces are still visible, like the front of the right shoulder:
What I’d probably do here is use Transparent Depth instead, so any ray that’s already passed through one transparent surface (any outside surface of the head) will see subsequent surfaces as transparent.
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This is a valid solution and works quite well. Thank you for your explanation 
In general and once again I am thinking: Why on earth has this to be so complicated… in Blender… again. Not you fault caterbk, in any way. It’s just my general desperation about why essential funtionalities in blender are often so complicated and different (in this case between render engines) and are only doable with a supertechnical approach and a deverloper-like mindset. I, as a “designer”, would never have come to this solution on my own.That being said: Thank you, community!
