Double sided SSS for flat surface not working

[VictorvdBrink]

I'm having an issue with getting subsurface to work corrctly for a simple flat plane that I'm projecting a custom foliage texture on. 

I'm only using 3 textures, color, opacity and normal. But I plugged the color into both the SSS color and SSS radius. 

I put the flat plane with the foliage material into a MASH network so I could distribute it over another mesh and create an ivy. 

However when I render the SSS color only seems to work from one side. Even reversing the normals doesn't seem to change the side that shows SSS. 

I've made sure that "thin walled" and "double sided" is checked in the material and in the attributes of the plane. And when I disable SSS altogether it renders both sides of the plane fine. 

Also it might be worth mentioning that I noticed for some reason when I go into the attribute editor of the material I all the SSS inputs are actually greyed out except for the weight. However it the Hypershade window I can still manually input the color texture into the SSS. I don't know what that is about to be honest. 

Here are some quick test renders that hopefully illustrate what I'm talking about.

With SSS:

Without SSS:

If someone could help me I'd greatly appreciate it. This is a portfolio project so I want it to be as spotless as possible. I'm sure I'm just overlooking something. 

[lee_griggs]

The SSS render looks correct to me. They should look darker in shadow. The render without SSS looks far worse to me. You can see a similar translucent effect with the paper planes here.

>However it the Hypershade window I can still manually input the color texture into the SSS. I don't know what that is about to be honest. 

The SSS attributes are greyed out because thin_walled is enabled. You can probably still connect maps, though. They just won't be used.

[VictorvdBrink]

Hi there. Thank you for your reply. Maybe I wasn't clear on what the issue is I'm seeing so I hope this will clarify. 

[VictorvdBrink]

Nevermind. I'm a dummy. It was my roughness that is causing the issue, SSS is working fine. I hadn't put in a roughness map yet, because I didn't think I'd need it. 

However it is leaving me with another issue, because I find it kind of odd that roughness is causing this issue. I'll try inputting a custom roughness maps to see if that helps. 

[lee_griggs]

Ok, if that doesn't work, post a simple scene here so we can look at it.

[VictorvdBrink · Accepted solution]

Alright. I'm starting to get the results now that I like. I disabeled thin walled and plugged the color into the radius via a color correction node so it gives me a bit more room to play with values. 

Using a custom roughness texture also seems to have worked. I think before the leaves were just reflecting way to much of the skydome light, and that made them look desaturated and bright. 

Also being able to adjust the SSS scale, so I can determine how much light is let through seems to be a good way to ge the desired result when viewing from different angles. 

The last thing I need to do that could improve things as well is to figure out how to get a better distribution of the leaves using my MASH network. I think its a bit to clumped up at some points, and the leaves are supposed to get less numerous when reaching the end of the vines. Which is also creating some issues. 

[lee_griggs]

Looking good! A diffuse_ray_depth >1 will help boost some light in some of those dark areas.

Maxime Jeanmougin also has a nice Bifrost ivy compound that could help add some detail to the scene.

[VictorvdBrink]

Thanks! You mean the ray depth in the render settings? I already have diffuse ray depth set to 3. I think in just need to add some extra area lights here and there.