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Cloth materials have a specificity in that they are made of fibers, mostly semi-opaque that put together end up being almost fully opaque.

They also tend to catch light from their edges due to the presence of many rebel fibers that pop out of the fabric material, as see on these reference photos:

 

This is not reproducible with a regular BRDF model without either cheating of actually modeling the fibers, for this reason the Arion BSDF has the Falloff parameters which helps in these cases.

The Falloff parameters are not physically-correct in any way, they are artistic controls added for this kind of material specifically so they are not too difficult to simulate.

 

Start with a default Arion BSDF material.

BRDF attributes
Fresnel IOR 1.51 0.0
Falloff 46.5 16
Color
Edgetint
Roughness | % 100
Bump | % 10

 

For the moment we will work on a textures-less material.

Define a Color value of your choice, in this example we have, again, picked the RandomControl red RGB (182,32,2) and enable the Falloff parameters.

BRDF attributes
Fresnel IOR 1.51 0.0
Falloff 46.5 16
Color
Edgetint
Roughness | % 100
Bump | % 10

 

I think you already start to see where this is going.

The Falloff parameters changes the linear Fresnel IOR interpolation for the front-facing (Color) and edge/grazing angle (Edgetint) parts of the object.

The default values are pretty extreme, fine-tune them until you have reached a pleasing result.
In our example values of 2.0 and 5.0 were picked, but it can be anything that looks good to you.

BRDF attributes
Fresnel IOR 1.51 0.0
Falloff 2.0 5.0
Color
Edgetint
Roughness | % 100
Bump | % 10

 

We need to tone-down the reflection by using a lighter shade of our red for the Edgetint.
In our example we have copied our red to the Edgetint parameter and lowered the color saturation to 140 and its lightness to 255, resulting in an RGB value of 255,138,115.

BRDF attributes
Fresnel IOR 1.51 0.0
Falloff 2.0 5.0
Color
Edgetint
Roughness | % 100
Bump | % 10

 

Just like with diffuse materials, it is advised to not use a Roughness of 100% as it looks unnatural.
In this example we have reduced it to 85%.

BRDF attributes
Fresnel IOR 1.51 0.0
Falloff 2.0 5.0
Color
Edgetint
Roughness | % 85
Bump | % 10

 

The next step is to do the same thing with textures.

Find a texture of your choice and plug it into the Color channel. Copy this texture to the Edgetint channel (or use an Arion Correction texture) and edit its RGB modifiers' Brightness property up.
In this example a Brightness value of 50% did the job.

BRDF attributes
Fresnel IOR 1.51 0.0
Falloff 2.0 5.0
Color <
Edgetint
Roughness | % 100
Bump | % 10
RGB modifiers
Invert
Gamma | % 0
RGB | % 0 0 0
Clamp | % 0 100
Brightness | % 50
Contrast | % 0
Saturation | % 0

 

The only thing that's left is some bump mapping and we're done.

Now lets compare without and with Falloff for the same material properties.

Without FalloffWith Falloff

 

By playing with the Falloff and the Roughness parameter, you can achieve different kind of 'fabrics' such as satin or silk.

Since satin or silk have a metallic aspect, you will need to raise the Fresnel IOR value a bit. We have used a value of 5 for these examples and lowered the Roughness to respectively 45% and 25%.

 

 

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