Subsurface scattering explained

Table of contents

• Mastering subsurface scattering in V-Ray ➔
• What is subsurface scattering ➔ 
• Why subsurface scattering matters for 3D artists ➔  
• The science behind subsurface scattering ➔ 
• Subsurface scattering vs. refraction ➔  
• Subsurface scattering shaders and tools ➔
• Components of subsurface scattering ➔
• V-Ray material SSS properties and their applications ➔
• Practical applications and case studies ➔
• Challenges and optimization strategies ➔
• Common SSS mistakes and how to fix them ➔ 
• FAQs ➔

Master subsurface scattering in V-Ray: understand it, use it, and optimize it for breathtakingly realistic renders

Light is more complex than it appears. The way it interacts with the world around us goes far beyond simple reflection — and capturing that complexity is what separates a good render from a truly convincing one. In this guide, we'll break down subsurface scattering from the ground up: what it is, why it matters, and how to use it effectively in V-Ray.

What is subsurface scattering?

Subsurface scattering (SSS) is the process by which light enters a translucent surface, travels inside the material, and exits at a different location from where it entered, or through the same point it entered. Instead of bouncing off the surface, incoming light penetrates the object, scatters in multiple directions within it, and re-emerges — often carrying a shifted color, softened edge, or warm inner glow.

When light hits human skin, it doesn’t reflect off the top layer — it penetrates several millimeters, bounces through tissue, fat, and blood vessels, and exits somewhere nearby. In fact, approximately 94% of the light is scattered beneath the surface, while only about 6% is reflected directly off the surface. The same physics apply to wax, marble, milk, and leaves.

In 3D rendering, SSS simulates this behavior. Without it, translucent materials appear flat and plastic-like in the final image. That's because the renderer only accounts for what happens at the surface, and not inside the material.

Why subsurface scattering matters for 3D artists

The difference between a render with and without SSS isn't subtle - it could be the difference between a material that looks real and one that immediately looks digital.

Consider human skin: less than 10% of light reflects directly off its surface. The rest scatters beneath, which is why skin has that soft warmth, why veins tint red light, and why ears and fingers glow when backlit. Without SSS, the result is painted plastic regardless of how good the texture is.

The same applies across materials:

• Wax glows orange near a flame as light scatters through its thin parts.

• Marble and jade get their depth from light entering, scattering, and returning from slightly different points.

• Leaves reveal their internal structure when backlit because light diffuses through thin translucent tissue.

• Food and beverages such as grapes, milk, fruit, and juice look appetizing because of how light interacts with their semi-translucent interiors.

One thing to note is that SSS does increase render time, but when used selectively on the materials that need it, the trade-off is well worth it.

The science behind subsurface scattering

Subsurface scattering occurs when light passes through a translucent surface like a glass of milk or the leaves on a sunny morning, is absorbed, scattered, and re-emitted.

To better understand this concept, hold your hand up to the light, and you will notice a warm glow around it, illuminating your veins and creases. In 3D graphics, if subsurface scattering is not applied, translucent objects like paper, wax, marble, and skin will look opaque and lack photorealism.

Subsurface scattering vs. refraction: what's the difference?

These two terms are often confused, but they describe different physical phenomena — and mixing them up leads to the wrong shader choice.

Refraction (or transmission) is what happens when light passes directly through an object, maintaining its direction with minimal deviation. Think clear glass or crystal. The material lets light through without much internal interaction. In V-Ray, this is handled through the refraction channel of VRayMtl.

Subsurface scattering is what happens when light enters a material but doesn't pass straight through. Instead, it bounces around inside, gets partially absorbed, and exits at the surface. The scattering distance and internal composition determine how far light travels before re-emerging, and the scattering color or scatter radius determines which wavelengths get absorbed along the way.

This is why red light scatters further inside human skin than blue or green — causing ears and fingers to glow warm when backlit. Refraction alone can't produce this because it doesn't account for what happens inside the material.

A simple way to decide which one to use:

One more distinction worth knowing: translucency sits between the two. A translucent material, like a lampshade or a thin leaf, allows light to pass through but diffuses it in the process. It's not as directional as refraction and not as deep as full SSS. In V-Ray, this is typically handled with the thin-walled mode in VRayMtl and VRay2SidedMtl when the object doesn’t have thickness. 

Subsurface scattering shaders and tools

V-Ray offers a complete set of tools to render subsurface scattering. Let’s explore them below.

Physical subsurface scattering shaders

On one end of the spectrum, for those requiring the ultimate accuracy, the V-Ray Material, a physical SSS shader, includes a brute-force random walk approach that closely mimics real-world light behavior. This method is analogous to that found in the vrayScatterVolume shader and is well integrated with the rest of the shading layers in the material.

The various modes available in both shaders allow for great flexibility and resource budgeting, depending on the desired outcome—from thin liquids to dense alabaster, they can simulate it all with accuracy.

Fast shaders for look development

For quicker look development, with minor concessions to accuracy, V-Ray also offers the industry-renowned ALShader, a fast shader that is ideal for quickly setting up the simulation of skin and other such complex, multi-layered SSS materials. Also based on brute-force random walk, it offers directional and diffusion profiles to better suit the user's needs for looks and speed.

Rendering considerations

For these shaders to work at their best, the user must account for the full complement of lighting, global illumination, and ancillary geometry (e.g., seeds inside grapes).

Speed-optimized SSS: the vrayFastSSS shader

Lastly, the vrayFastSSS shader uses the seminal Jensen approach to quick sub-surface scattering calculations. (Refer to Jensen's seminal paper from 2001). It doesn't require global illumination, nor does it take into account the geometry lying below the shader's surface, but it can compute very convincing approximations of subsurface scattering in thick liquids, plants, and greenery in general, and even distant characters. A simplified version of this technique, such as collapsing multiple blur passes into a single shader pass, can make it more practical for real-time applications, though it may reduce some detail or flexibility.

Components of subsurface scattering

Subsurface scattering can be broken down into different components based on how light interacts with the interior of a material, with light diffusing within the material being a key aspect. These interactions determine the softness, depth, color bleeding, light directionality, and translucency. While some materials are better suited for specific effects, you can experiment with all SSS components using just one type of material, like the skin on a human face pictured in the comparisons below.

Forward scattering

Forward scattering occurs when light enters an object and continues moving in the same direction as the original light ray. This is typical for thin or lightly translucent materials like leaves and skin, allowing light to exit on the other side.

Back scattering

Back scattering occurs when light enters the surface of an object but is reflected back toward the direction it came from. It is more common in denser or more complex materials, where light bounces around chaotically beneath the surface. Picture the subtle softness on the lit side of human cheeks or the creamy look of yogurt.

V-Ray material SSS properties and their applications

Achieving SSS in V-Ray is not a single toggle. It's an effect that emerges from a combination of material choice, object properties, and lighting conditions. Understanding how these elements work together starts with knowing which shader to reach for and why.

Choosing the right V-Ray SSS shader

V-Ray offers several SSS shaders, each optimized for a specific type of material. Picking the right one up front saves significant time, and using the wrong shader makes results harder to dial in, regardless of how much you adjust the settings.

• Thin, flat objects — leaves, paper, fabric: use VRay2SidedMtl or a V-Ray material with SSS and the ‘Thin-walled’ option enabled. Use the ‘SSS amount’ to control the amount of light passing through (values between 0.3 and 0.5 work for most of the cases), and the ‘SSS color’ to adjust the color of the light passing through.

• Liquids, plants, background objects, or early look development: use VRayFastSSS2. The fastest option — produces convincing SSS without requiring global illumination. Accuracy is lower than VRayMtl, but for anything where speed matters more than precision, it's the right call.

• Human or creature skin: use VRayAlSurface. Purpose-built for skin, with three independent SSS layers for surface color, subsurface muscle tone, and deeper layers like veins — plus two reflection layers for base skin and oil/sweat. No other shader matches this level of control for realistic skin.

• Solid translucent materials — wax, marble, jade, food: use VRayMtl with volumetric translucency. The most physically accurate option for solid objects. Enable refractions, set translucency to volumetric, then use fog color and scatter color to control how light moves and which wavelengths get absorbed inside the material.

• Complex hybrid materials — ice, gems, layered effects: use VRayScatterVolume inside a VRayBlendMtl. A brute-force, unbiased SSS layer that, when blended with other materials, lets you build complex results that need volume scattering as one component of a larger shader stack.

In V-Ray, a shader is the material that governs these interactions. A shader determines how a material behaves. Below are several V-Ray shaders that can be used to simulate different subsurface scattering (SSS) effects along with their unique characteristics.

Using Volumetric Scattering (VRayMtl)

Jade/Marble Dragon

1. Apply a standard VRay material to the object.
2. You could give it a little bit of reflectivity by setting the reflection color to mid-gray.
3. Enabling refractions is an important step in enabling the VRay material's translucency capabilities. So, let’s set the refraction color to white.
4. Next, we need to choose the translucency type. Let’s go for volumetric.
5. By playing with the fog color and the depth, we can adjust the overall color of the material and its softness. Using the scatter color, we can set the color of the scatter.

Using VRayFastSSS2

Candles

1. Apply VRayFastSSS2 to your object—ideal for skin, wax, marble, and other organic materials.
2. To create a wax material, we could play with the subsurface color and the scatter color. For example, we could set the sub-surface color to a yellow color, which is going to be the main color of the candle. And set the scatter color to orange, which is going to be visible in the thin parts of the candle geometry. This way, in the area around the flame of the candle, it’ll look more orange.
3. Next, we can play with the scatter radius parameter. In the case of wax, it is a good idea to allow the light to scatter deeper beneath the surface, so 2 cm should suffice.
4. Finally, for creating a material such as wax, we need more of a forward scattering approach, so let’s set the phase function to account for that to 0.8.
   
   
   

Using VrayAlSurface

Woman closeup

1. Apply VRayAlSurface to your object—this shader is versatile and designed for realistic skin and layered materials.
2. Set the diffuse color for the overall look of the material. It could be a flat color or a texture map. In this example, a texture map was used.
3. Make sure you enable subsurface scattering by setting the “SSS mix” parameter to 1.0
4. You could experiment with the parameters and colors of the three SSS layers to achieve the type of skin you’re after. The default values are getting pretty decent results too.
5. If you have a normal or bump texture, you could also plug it in to give your material an extra level of detail.
6. Finally, you could adjust the reflectivity of the material by playing with the reflection color and roughness parameter.
   
   

Using VRayFastSSS2

Forward/Backward/Isotropic Scattering

1. Apply VRayFastSSS2 to your object—ideal for skin, wax, marble, and other organic materials.
2. Set an overall color or texture that would serve as a base color.
3. You could play with the scatter color to adjust the subsurface scattering color of the material. It is mostly visible in the thin parts of the geometry. (Ears of a character, for instance).
4. By adjusting the scatter radius parameter, you can control the depth of scattering light inside the material.
5. Finally, you can switch between several types of scattering using the phase function parameter. If the phase function parameter is set to 0 that is called isotropic scattering. It means that light scatters uniformly in all directions. A value of -1.0 would trigger backward scattering. In this condition, most of the light bounces back to the direction it came from. And finally, a value of 1.0 would trigger forward scattering. In this condition, the light scatters predominantly forward:

Using VRayScatterVolume

Icy sphere

1. The VRayScatterVolume material is designed solely as a brute-force option for SSS to produce an unbiased result. When used as a base material in a VRayBlendMtl, it can create complex materials with a subsurface scattering base. For example, we could create an ice material using the VRayScatterVolume.
2. We need to set an overall color to serve as a base. We could choose light blue.
3. Next, we can experiment with the sub-surface and scatter color until we get the result we’re after.
4. We should also experiment with the scatter radius parameter to control how deeply the light scatters under the surface.
5. Finally, we can adjust the phase function parameter. To create ice, we could set the phase function parameter to 0.15 to slightly favor forward scattering.
   
   
   
   

Using VRay2SidedMtl

Autumn leaves

1. The VRay2SidedMtl material is designed solely as a brute-force option for SSS to produce an unbiased result. When used as a base material in a VRayBlendMtl, it can create complex materials with a subsurface scattering base. For example, we could create an ice material using the VRayScatterVolume.
2. We need to set an overall color to serve as a base. We could choose light blue.
3. Next, we can experiment with the sub-surface and scatter color until we get the result we’re after.
4. We should also experiment with the scatter radius parameter to control how deeply the light scatters under the surface.
5. Finally, we can adjust the phase function parameter. To create ice, we could set the phase function parameter to 0.15 to slightly favor forward scattering.
   
   
   

Practical applications and case studies

Digital portraiture and character design

An excellent example of SSS in action is the way backlit ears appear to glow in their thinner areas, revealing how light penetrates and scatters through these regions. Due to its ability to produce a remarkable level of realism, SSS often proves to be an invaluable technique for creating more detail in lifelike skin textures in digital portraiture and character design.

Game rendering and immersive environments

Some real-time game rendering software can't afford the computational cost of true volumetric SSS, so it uses clever approximations instead. The three most common techniques are screen-space diffusion, which blurs lighting in screen-space buffers to simulate scattering; pre-integrated SSS, which pre-computes scattering results into lookup tables based on surface curvature and shadow penumbras; and texture-space diffusion, which renders and blurs an irradiance map in UV space before applying it to the final image.

The trade-off compared to offline renderers like V-Ray is real — these methods can miss scattering data behind occluded surfaces, and back-side transmission often requires additional thickness maps to fake convincingly. But for real-time character design and immersive environments, they produce results that are remarkably close to path tracing at a fraction of the cost.

Product visualization in advertising

The technique is also in product visualization, particularly in advertising for cosmetics and food. SSS enhances the look of skin creams, lotions, and gels by giving them a soft, translucent quality that evokes richness and youth. When using 3D product design rendering software for visualizing food, SSS adds a high level of photorealism to items like candy, fresh fruit, and beverages of all sorts by simulating how light subtly scatters beneath their surfaces, making them appear more appetizing.

Case study: The wooden metropolis project

The Wooden Metropolis project not only serves as a great case study of SSS in V-Ray but also demonstrates the powerful social impact 3D visualization can convey. An advertisement for NGO Robin Wood, the project draws attention to the alarming rate of deforestation by addressing urbanization and highlighting that an area of woodland larger than New York City is lost every day. PX Group’s team relied on V-Ray's Fast SSS2 material to authentically replicate the appearance of fresh wood.

"We began by looking at the tiniest piece of the puzzle: when a tree is split, the fresh splinters appear somewhat shiny, almost like porcelain or white chicken meat. On closer observation, reddish light gets scattered inside the splinter tips. In nature, this translucent effect is very subtle and most apparent when those splinters are lit from behind. We figured the most obvious shader to achieve this effect was V-Ray's Sub Surface Scattering material, fast SSS2."

Christian Sturm, 3D Artist

Challenges and optimization strategies

SSS is a powerful technique, but it's also one of the more unforgiving ones. Small oversights in your setup can produce results that look obviously wrong, and tracking down the cause isn't always straightforward. Getting the basics right before you start saves a lot of troubleshooting later.

Before you start: SSS setup checklist

SSS is one of those effects where preparation matters as much as the settings themselves. Before touching any shader parameters, run through these first:

• Check your scene scale. SSS scatter radius is measured in real-world units. If your object isn't modeled at real-world dimensions, no amount of parameter tweaking will produce correct results.

• Clean your geometry. Overlapping faces, open edges, unwelded vertices, and missing thickness will all break SSS. The effect depends on the renderer being able to calculate what happens inside a closed volume.

• Have a reference image ready. Real-world references like a photo of skin in backlit conditions, a candle near a flame, a marble surface, give you a target to match and prevent you from over-adjusting settings blindly.

• Set up your lighting first. SSS is highly dependent on light direction and intensity. Backlit setups will reveal scattering far more than flat frontal lighting. Establish your light source before evaluating any SSS results.

Common SSS mistakes and how to fix them

Even with the right shader selected and a clean scene, SSS has a handful of failure modes that come up consistently. Here’s what causes them and how to fix each one.

• The scattering looks washed out or invisible. Almost always a scale problem. SSS radius is calculated in scene units, so if your object is modeled at the wrong scale, the scatter distance will be either too large (everything glows) or too small (no effect visible). To fix this, match your scene units to real-world dimensions and adjust the radius to reflect the actual size of the object.

• The material looks plastic or flat despite SSS being enabled. This is usually caused by missing or weak GI. VRayMtl and VRayAlSurface need global illumination to calculate internal light bounces correctly. Fix this by enabling GI and check that your light intensity is strong enough (SSS is subtle under weak lighting).

• Skin looks waxy or overly translucent. This often happens when higher values for the scatter radius or SSS intensity are used, making the effect too strong. Also when the scatter radius is too high, or the SSS color is too saturated. Real skin scatters light over a very short distance, typically 5–20mm, depending on the area. Fix this by reducing the scatter radius and desaturate the SSS color slightly. Use VRayAlSurface’s three independent layers to separate surface color from deeper scatter.

• SSS breaks at geometry edges or produces artifacts. Open geometry, unwelded vertices, or missing thickness are common culprits here. SSS requires a closed volume to calculate correctly. Check for holes, overlapping faces, and non-manifold geometry before adjusting any shader settings.

• Render times spike significantly with SSS enabled. SSS is computationally expensive, especially with VRayMtl volumetric mode. Use VRayFastSSS2 for background objects or any material where the SSS detail won’t be visible in the final image. Reserve volumetric SSS for hero materials in close-up shots.

Real-time rendering and SSS

Ray-traced SSS in offline renderers like V-Ray uses physically based rendering (PBR) principles, path tracing and Monte Carlo methods to simulate how light genuinely scatters inside a material. It calculates thousands of light paths through the volume to produce a physically accurate final image. Real-time renderers like Enscape take a different approach: they use simplified, GPU-optimized approximations that sacrifice some physical accuracy in exchange for interactive framerates, and tuning ambient lighting and exposure in Enscape becomes critical to getting convincing results when using real-time rendering software like Chaos Enscape. Some real-time techniques also utilize the red channel of normal maps to simulate diffusion effects, influencing how diffuse subsurface scattering is represented in rendering human skin or detailed surfaces, similar to how translucent materials are handled in Enscape.

The gap between the two is narrowing fast. Modern real-time engines now support screen-space and texture-space diffusion techniques that produce convincing SSS for most materials. But for close-up hero shots, complex skin rendering, or any scene where subsurface detail is the focal point, offline path tracing still delivers the best results.

To wrap it up

Substance scattering is an excellent tool for adding an extra level of photorealism to your renders. It takes into account the physical properties of light and the way it interacts with each unique object, preventing them from looking plastic-like and creating a realistic representation of the scene’s surroundings. We encourage you to experiment and play around with the different shaders in V-Ray and explore which ones incorporate best into your workflow.

FAQs

Should I use subsurface scattering?

You should definitely use SSS, especially for translucent objects. It can help make a huge difference in creating realistic skin, wax, marble, liquids, foliage, and more.

What objects have subsurface scattering?

Any semi-translucent material where scattered light diffuses inside — skin, wax, marble and jade, fruits, milk, juice, leaves are just some examples.

How can I improve my renders using subsurface scattering?

Use SSS for the right materials, and experiment with different shaders to see which one gets it just right.

Does enabling subsurface scattering increase render time?

Yes, but if used smartly, not by much. You can manage performance by using it selectively, and keeping in mind it’s a trade-off between time and quality.

Why is subsurface scattering important for 3D artists?

SSS mimics how light interacts with real-world materials through scattering. Without SSS, materials lack depth and look artificial — skin looks plastic, wax looks flat, and characters, close-ups, and product shots lack photorealism.

What is the difference between subsurface scattering and diffuse reflection?

Diffuse reflection happens entirely at the surface with light hitting the material and bouncing back without penetrating it. Subsurface scattering goes deeper: light enters the material, travels through it, and exits at a different point. That internal journey is what produces the soft warmth in skin and the depth in marble. Effects that diffuse reflection alone can never replicate.

How does subsurface scattering differ from translucency and volumetric scattering?

SSS describes light entering a material, scattering internally, and exiting nearby. Translucency is simpler. Light diffuses through a thin material without deep scattering, like a lampshade or leaf. Volumetric scattering describes continuous light interaction inside a medium like fog or smoke. In V-Ray, these map to different shaders: VRay2SidedMtl for translucency, or a V-Ray material with refraction and volumetric scattering enabled.

What SSS parameters produce realistic human skin in V-Ray?

Use VRayAlSurface. Keep scatter radius between 5–20mm as real skin scatters over a short distance. Use the three SSS layers to separate surface tone, subsurface warmth, and deeper tissue. Slightly desaturate SSS colors compared to your reference. Enable GI as VRayAlSurface requires it to calculate skin layers correctly.

What is the difference between BSSRDF and BRDF, and why does it matter for skin rendering?

BRDF only models light interaction at the surface. BSSRDF accounts for light entering at one point and exiting at another — what physically happens in skin, wax, and marble. A BRDF-only approach produces flat, unconvincing results for these materials. V-Ray's SSS shaders are all BSSRDF-based, which is what makes accurate translucency possible.