I was recently asked about setting up fabrics materials, so here is a super short guide:
1. Here is our curtain model with a clay material. It looks pretty boring.
2. The first step is to add a falloff map in Fresnel mode as diffuse color to get the highlights on edges which you can observe on fabrics in real life because they are fuzzy and there is some complex light scattering going on in there. Obviously you can use bitmaps for this (darker + lighter version of the same texture).
3. The next step is adding some translucency, to allow the light to pass through the material. Lower fraction values mean the effect will be more subtle. Color is set to white here, which is wrong.
4. Setting translucency color to something more natural makes the material look much better. Basically if you cut the fabric, this is the color of the inside of it, while the diffuse color is the color of it's surface.
5. If we move the light around, we can see that it now passes through the object, and you can clearly see that in the shadows.
6. Now let's add reflectivity (this is optional). With default values the material looks like it's frozen.
7. So let's lower the glossiness to ~0,2. Remember that virtually all materials in real life have some reflectivity, so if you want your scene to be realistic, this is probably the way to go. Since we are following the PBR guidelines, we can just leave reflection level at 1, and Fresnel IOR at 1,52, and forget about them. If you need different appearance of the reflections, adjust glossiness only.
8. Next step is adding a bump map. This will define the structure of the fabric, and also make it look a bit thicker and heavier. I used a procedural checker map, but using bitmaps would be probably better.
9. If you want your fabric to be transparent, you can adjust opacity. I just slightly decreased it to 0,95 here to see what's behind. You can also use falloff map here to get thicker-looking edges, or use a patterned bitmap.
10. Now if we place the light behind the curtain, we will be able to actually see it, but other effects such as translucency and bump will be visible as well.
Scene in Max 2016 format:
https://forum.corona-renderer.com/index.php?action=dlattach;topic=17423.0;attach=70543
