It's very simple to do. There should be a Mix Material which can combine two materials Primary and Secondary. There is also a port Primary Amount. So you should connect CentiLeo Surface Side node to this "Primary Amount" port.
After that Primary become Front and Secondary become Back material.

Thanks for files to thrimanakatha, ssjenforcer
Working to fix the issue. At the moment I have found that if the object is tesselated (more polygons) more the artifact goes away. For example adding subdiv removes the artifact. But I need to fix it without this workaround.

If you use CentiLeo node materials then each material has several layers: Reflection1, Reflection2, Transmission, Diffuse, SSS, Translucent, Alpha. Each layer has it's own paramers such as weight, color and roughness, ior and others. Additionally there is a tab called "Inputs" it has the list of all material layers that you can enable/disable with a flag. This is a standard thing as in C4D native materials.
If you use Menu based old style CentiLeo materials (in Cinema 4D older than R21) then there is a tab called "Basic" where you can enable/disable all material layers.

No yet, there are plans to make a library of materials. However, current material engine is pretty much similar to C4D native or Corona or Octane. Same values of material parameters produce the similar result

Hi ron134,
To get rid of noise that you call grainy you have to increase the number of render iterations in CentiLeo render settings.
Also CentiLeo uses own materials (CentiLeo material and all sorts of textures/shaders). And it uses Cinema 4D light sources as the base but they need to be connected with CentiLeo light tags that extend the base light source with several extra settings available for CentiLeo.
Sure we need to launch a complete documenation about the software, we will do it after finishing the next technical release

thrimanakatha, can you send me this scene file with HDR please?

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thrimanakatha wrote: 1. I did a test with a sphere with a glass material applied to the front half and diffuse material to the back half. Placed a cube inside the sphere and rendered. The GI flickering is there, so the geometry is not causing the issue. 2. Added thickness by extruding the sphere, the issue is still there.

Interesting finding! Can you please give me this scene for test? I am very curious. What was animated there? A camera?

Thanks for another case! Actually there can be z-fighting where two surfaces are aligned in the same positions and hence even without any glass they alternate and produce some flickershit. I will look at your files.

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thrimanakatha wrote: What about the next update?

Working hard on the next release. Yes it's quite long already, but these perfromance things will bring a good value for CentiLeo!

Well, the area light doesn't shine behind it. Actually from regular geometry objects the Omni light source is the best for matte shadow tuning. And you can exclude such a light source from shining to the other objects by setting zero for the multipliers of Reflection, Diffuse, Transmission and other layers. Only make Shadow Weight non zero

Thanks for files and advices! I have detected the issue. It has 2 issues to consider:

1) The car windows are made of glass material and this glass geometry is too close to the surrounding non-glass parts. There is some small gap between rays launching from the windows objects and the gap is too small between objects. The geometry seems to be animated a little bit for a fraction of milimeter and it's also lowpoly. So we see the windows objects slight poping that affects the interior and creates the effect of flickering.
So the first solution would be to increase the distance between windows and other car parts.

2) The second solution would be for me to fine tune the computation of this small gap that's used for rays launching from the surface.

Actually by default the material list in R25 isn't visible (I mean all that material balls at the bottom). But the selection may be active if the material it's just created and you edit it.
As for IPR it doesn't select/deselect anything, only change the statusbar when geometry updates are ongoing.
My version is R25.010. Will update to R25.25 to see what's there.

I am testing the issue right now with a scene composed of single cylinder, centileo node material + noise + gradient or anything else. In R25 with CentiLeo IPR active.
I add or remove any node alone e.g. a noise or gradient. And the rest material node system remains there. Ctrl+Z/Y works fine.
In fact CentiLeo IPR is not related to the node system in either way, they don't depend on each other.

Can you check if your material is selected in the Cinema viewport? It may happen that your entire material is selected in the list of materials and once you click "delete" this selection is removed as well together with selected gradient node. It can really be a forgotten selected material in the list, just deselect it.
What's your Cinema version?

Yes, you can combine the bump map branch and normal map using Math.Add node or any other texture.
In fact everything connected to Bump slot of material is considered as black and white bump map.
To use normal map encoding of centileo bitmap (such as blue for unchanged normal and red/green gradients for normal vector changes) you have to check "Is Normal Map" flag in centileo bitmap. Then internally the normal map will be converted to black/white image ready to connect to the Bump map slot. And you will be able to combine it with other bump maps, adding, mixing, multiplying, etc.
Also keep in mind that converted bump maps (from normal maps) may have negative values in shader network internal opeations, because they show relative change of normal vector. These negative values are relative to unchanged normal and resolve for material correctly. But you have to consider this fact when for example you Color Correct them and probably want to apply some clamp for bumps.

Send me a scene to info@centileo.com pls? I will check what's wrong there

thrimanakatha, thanks for giving the list of extra potential reasons of that flickers. Indeed the noise removers / denoisers can produce the issues on low sample counts

It's very lowpoly. Can you add a Subdivision Surface Object on top of lowpoly objects and apply 1-2 steps of subdivs?

It's certainly hard to notice any flicker based on still images. I think the a noisy and lowres video can help.
Actually there should be no any flickering because CentiLeo is unbiased. The reflecion may produce bright effects from the sun.
Also the surface of the car needs some more subdivs to get smoother however this is probably not the source of flickers.

You are right, the Sky+Environment tag supports only spherical lattitude/longitude HDRI mapping, it doesn't support mapping to camera space like tha Background object. That would be easy to modify.
At the moment background mapping can be implemented using a workaround e.g. using a plane object with material with you background and this plane object is placed in front of camera and reacts to camera movements. I think it's possible to do this with scripts but some extra skills would needed. Anyway I have to do it in a simpler way

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ssjenforcer wrote: Also, were you able to reproduce the shadow catcher bug with Area and spot lights? I assume there is still work to be done with light settings?

I have replied in that topic. Not a bug, but a specific detail of light shape. Actually I need to make light includes/excludes from illuminating the objects.

Actually this is the right finding that shadow catcher weights only for Omni, Infine lights sources and Sky+EnvMap tag.
The others lights like Area and Spot don't support casting to the shadow catcher because they have limited directional lighting, e.g. they don't lit the scene behind them. This would create unneceassary shortcomins.
On the other hand the Omni light is good, you can place it somewhere and tune the radius to get the neceassary postion and shadow softness.
Also why your shadow catcher object plane is so small? Usually it should be larger.