Raytracing Translucency: Opaque glass interreflection?

Hey everyone,

I am trying to control the visibility of translucent objects in the reflection of another translucent object without any success. Basically I’d like glass windows to be invisible in the ray traced reflection of other windows. Currently, what ever i tried, it always shows up opaque.

This is the current class material setup:

I looked around on this forum and reddit, expecting this to be a bigger issue in arch viz, but surprisingly didn’t find much info on this.

I’ve gone through all settings in materials, post process volume and static mesh component, that i can think of with no success. Tests were done in 4.27, 5EA2 and 5 Preview, using both raytracing and lumen. Translucency is always set to Ray traced, to achieve sharp reflections, which is something lumen can’t deliver yet.

Interestingly, ray traced reflections of opaque surfaces like chrome ARE treating translucent objects the way i hope to achieve, even offering a checkbox to exclude translucent objects from reflections. This has no effect on the reflections of translucent objects though.

Has anyone else faced this problem before and can offer a solution, hack or workaround?

Are you using UE5?
Check this:

Translucency is not completely supported with Lumen.

These are known issues since the first ue5 release and it is currently not defined if this can/will be fixed.

Even in 4.27 - without Lumen, using just raytracing - the reflected glass surface renders opaque, rather than invisible/translucent.

Independent of UE4/5, changing reflection type or settings in PP volume seems to have no effect on the reflection of translucent surfaces.

Setting translucency type to raytracing on the other hand not only enables raytraced refraction but also raytraced reflection (which felt a bit misleading to me, but ok).

Either way, the opaque reflection of chrome using raytraced reflection seems to be able to ignore translucent surfaces. I guess I am just hoping to find an option or workaround to have raytraced translucent reflection do the same.

For reference, this is what it looks like using lumen with raytraced OR raster translucency:

(The lumen+raster renders with the lowres reflection that is expected from the current limitations as explained by Epic)

I posted a similar question, but I only want to use 4.27 in my case https://forums.unrealengine.com/t/question-regarding-raytraced-reflections-of-translucent-objects/616687