What Is Subsurface Scattering (SSS)?

Subsurface scattering defined

Subsurface scattering (SSS) describes light scattering beneath a material’s surface. Light enters, scatters and is partly absorbed; some emerges at a different location. This can visibly contribute to the appearance of wax, soap, certain plastics or stone. Whether you need to calculate it separately in a rendering depends on the material, its thickness, the lighting and the framing. Shader controls and their meanings vary between applications.

Why SSS can matter in product imagery

• Material appearance: Some surfaces look too hard without appropriate scattering; others look too soft with excessive SSS. Use the actual sample as your reference, rather than making every edge glow.
• Image series: A documented material setup helps when reusing it in stills and animation. Different lighting and output settings still need checking.
• Home and living: Light transmission can matter for soap, candles, thin porcelain or certain stones. Leather, coatings and lampshades need assessment of their particular construction. See physically based rendering for the foundations.

How subsurface scattering works

Some incoming light is scattered inside a material; some is absorbed. Light can therefore emerge at a different point from where it entered. A BSSRDF describes this transport between different surface points. A foundational historical paper is A Practical Model for Subsurface Light Transport by Jensen, Marschner, Levoy and Hanrahan (2001). Its diffusion model is not the only method used today.

SSS, transmission and thin translucent surfaces

Methods for offline and real-time rendering

The Unreal Engine documentation on subsurface profiles describes one real-time approach. For web viewers, check which material features both the exporter and viewer support. An engine setting does not automatically transfer to every web format.

Setting up SSS for a product material

1. Gather references: Examine the physical sample under known lighting from several directions. Record its construction and wall thickness.
2. Build the base material: Set up base color, surface detail and reflection. Avoid unintentionally including lighting in the color texture. Ordinary metal surfaces are not treated like wax with SSS.
3. Understand scattering parameters: Radius or mean free path describes a scattering distance, not simply wall thickness. Model scale and units must be correct. Color and scattering distance may be coupled differently between shaders. The Arnold OpenPBR subsurface documentation explains one model.
4. Check surface reflection separately: Roughness and index of refraction affect the boundary surface. Do not adjust them arbitrarily to hide incorrect scattering. Learn more about depicting materials and surfaces.
5. Test light and camera: Backlighting and side lighting can reveal differences. Also evaluate the material in the intended image setup.
6. Compare: Check edges, color transitions and detail against references. If they differ, review geometry, scale, shader and output separately.
7. Plan outputs: Materials and lighting are part of producing image series and variants in our 3D rendering studio. See product visualization and surface digitization. A surface scan does not automatically capture every internal scattering property.

Assess the material instead of copying starting values

A material name alone does not provide suitable SSS settings. Composition, pigmentation, finish, thickness and scale affect the visible result.

• Wax and soap: Check transmission and color transitions in the actual sample. Not every product scatters warm light or scatters to the same degree.
• Plastics: Distinguish transparent, translucent and heavily pigmented plastics. A soft plastic does not automatically need more SSS.
• Ceramics and porcelain: Consider the body, glaze and wall thickness separately. Not every ceramic is visibly translucent.
• Marble: Account for stone type, thickness and surface finish. Roughness is not necessarily low.

Common issues to investigate:

• Too soft or waxy: Check scale, scattering distance and material model before changing individual parameters and comparing with the sample.
• Gray haze: Check input color spaces, base color, lighting and output transform. Changing the scattering color is not always the answer.
• No visible transmitted light: Check whether the physical material is translucent in the same lighting and viewing conditions. Do not add an effect just to exaggerate edges.
• Unwanted color casts: Compare material color, scattering parameters, light color and color management and tone mapping separately.

Material questions for home and living products

Subsurface scattering FAQ

When does a material need subsurface scattering?

When scattering beneath the surface visibly contributes to the material in the intended image. This can apply to wax, soap or certain plastics and stones. The material name alone does not decide it. Check the sample, its thickness and the lighting. A lack of edge glow from one viewpoint does not prove that no scattering occurs.

How do I determine SSS radius or scale?

First check model scale, scene units and the shader’s definition of the parameter. Scattering distance is a material property, not the same as wall thickness. Geometry affects how much light can emerge. Compare gradually against references under defined lighting; there is no universally suitable millimeter value.

Why does plastic look too soft or waxy?

Possible causes include an unsuitable scattering distance, incorrect scale, inappropriate material parameters or lighting. Check these separately. Simply increasing roughness may hide the issue while also changing surface gloss.

How do I use SSS effectively in real-time applications?

Use a method supported by the target system and test it on the intended devices. Profile and screen-space methods have their own limitations. Compare material appearance and computation in representative views. A low number of SSS materials or a particular radius does not guarantee a stable frame rate.

Which textures does an SSS material need?

That depends on the shader and material. Some parameters can be constant values; not every material needs normal or thickness maps. Color textures, roughness and any scattering parameters serve different purposes. A thickness map controls only the functions provided for it by the shader and does not generally replace geometry.

How do I check color and material appearance in the output?

Compare the rendering with agreed product and material references under known lighting. Check input color spaces, the view transform and the export profile. Interactive models also depend on the viewer’s material model and lighting. Matching file formats or an sRGB export does not guarantee the same appearance on every display.