TurboTips: V-Ray FastSSS2 Material, Part 1

by Calvin Bryson

The following is an in-depth guide to the regular V-Ray Blend Material. In this series, we will cover the theory behind many of the features of the material.  We’ll also show specific examples of settings and give you some tricks to use. While the images used are from 3ds Max, the same concepts and settings can be used for V-Ray for Maya. Currently, the SSS materials in V-Ray for C4D behave differently, so this tutorial will not be as valuable for C4D users.

The V-Ray FastSSS2 Material is designed for creating translucent materials (ones that scatter the light inside the object). Some common examples are: skin, marble, wax, milk, etc.

Compared to the “translucency” option in the regular V-Ray Material, it has a far better sub-surface scattering model (SSS).  It is faster and much more advanced. For this reason, it’s preferable to use the FastSSS2 Material whenever you need to make a translucent shader.

Settings

Since this material works in a slightly different way than other V-Ray Materials, let’s look at its settings and some examples of how they work.

Presets

You’ll notice that there are a few presets. These are pre-defined materials that you can choose from a drop-down menu and quickly use in your scene.

They do need to be customized with your own maps to look their best (colors, bump, reflection, gloss). So look at them as more of a starting point than a finished material. Perhaps the only ones that are good “as is,” would be the Milk presets, since it’s a liquid and you may not need any maps.

Prepass Rate

Next, let’s look at the Prepass Rate value. FastSSS2 calculates the distribution of light within an object using something similar to the Irradiance map, so this parameter sets how detailed we want this calculation to be. For most cases, you can leave it at -1 for optimal speed/quality; for test renders and objects without small details, bring it down to -3 or -2; but for very detailed objects that show some problem areas, try bringing it up to 0 ~ 1.

Scale

Scale controls the depth of the SSS effect. Since this material uses real world units to calculate the final result (you can set the scatter depth in cm a bit further down), this is an easy way to quickly turn up or down the depth. Quite simply, Scale 5 gives us Scatter Depth*5, etc.

IOR

IOR is the same old Index of Refraction that we are so familiar with. Here are some general guidelines:

  • Water based materials (Milk, Juice, Skin, etc.): set it to 1.333

  • Stone/Marble: 1.5~1.6 works best

  • Glass: 1.6~1.9

  • Plastics: 1.45~2.45. This parameter affects both (the Refractions [SSS] and Reflections). There is no way to unlink them currently.

 

Options

Before we proceed with the Diffuse and SSS layers (in the next part of this series), let’s check out Options. The most important things here to adjust are the Single Scatter type, Subdivs and Depth.

Single Scatter

There are 3 types of Single Scatter you can use: Simple, Solid and Refractive. These are all used for specific types of materials.

  1. Simple is the quickest to render but is also the least accurate. It’s great if the material doesn’t let in a lot of light, just a little bit (skin, plastic).

  2. Solid mode is best to use for materials that let in a lot of light, but at the same time are quite opaque, like translucent stone, milk, or wax.

  3. Refractive mode is for those materials that also have visible refractions and you can see through them relatively well- things like foggy glass, murky water, etc. This mode also makes the shadows transparent.

 

Subdivs & Refraction Depth

Subdivs and Refraction depth work much like regular V-Ray materials. Increasing subdivs cleans up the noise in the translucent areas; refraction depth controls how much the light bounces around. In general, you can leave these settings at their default values. If they need to be optimized for a particular scene (say, if an object is very refractive and not very opaque), you may try increasing the depth to be sure there are enough bounces to make it look realistic.

Most of the time, the rest of the settings in this section work just fine, as they are. If the render appears too blotchy, you can play around with the prepass blur value. Higher values will blur the scattered light more, though decreases accuracy.

Next week, we will continue this series with a talk about Diffuse and SSS Layers, the most important (and often the most confusing) part of the FastSSS2 Material.  If you have any questions about this week’s tutorial, please feel free to discuss it with us in the comments below.

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This series of tutorials was made with our friends at Viscorbel.  This is the final part in our series on V-Ray Material, but be sure to stay tuned to our social channels for our next series!

If there are any topics you’d like to see in a future edition of  TurboTips, let us know in the comments below, or Tweet your question to @TurboSquid with hashtag #TurboTips.

One Response to “TurboTips: V-Ray FastSSS2 Material, Part 1”

  1. Yegor Tsyba says:

    In Vray2 SSS2 work sucks on the small or distance objects, and now way to inprove it.
    Only in Vray3 was added sampler to control it.
    So its no so easy to use it in stock models that must works in Any situations.

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