Overview

The OpenPBR material is a physically based über-shader that presents as a standardized combination of the Autodesk Standard Surface and the Adobe Standard Material models. It is hosted by the Academy Software Foundation (ASWF) and organized as a subproject of MaterialX.

More information about the history and design can be found on this page detailing the OpenPBR Surface specification.

 

The OpenPBR material is made up of several layers.

• Base: The base layer sits at the bottom and can be configured to simulate many material types. It can represent a dielectric or metallic material and is responsible for the primary reflection layer. This is controlled by the Metalness parameter found in the Base parameters group. Normally materials are either fully metallic (Metalness 1) or fully dielectric (Metalness 0) but the OpenPBR material also supports a mixture when Metalness values fall between 0 and 1.

  • Metallic: When Metalness is used, reflections take on the Base Color and the Specular Color controls the color seen at glancing angles. Primary parameter groups are Base and Specular.

  • Dielectric: When a material is non-metallic it can be set up to represent the three main conditions covered below, but blending between them is possible by adjusting their relevant weights.

    • Glossy-diffuse: An opaque dielectric material that's good for many common materials that don't exhibit significant light scattering or transmission like wood and stone. Primary parameter groups are Base and Specular.

    • Subsurface: An opaque dielectric material that heavily scatters light internally like skin, plastic, marble, and wax. Primary parameter groups are Base, Specular, and Subsurface.

    • Translucent: A dielectric material that transmits and refracts a significant amount of flight and one that is more transparent than a subsurface material. Primary parameter groups are Base, Specular, and Transmission.

• Thin-Film: A very thin dielectric layer, measured in micrometers, between the base and coat layer used to represent the colorful effects as seen with soap bubbles, insects, and oil mixing with water.

• Emission: A light emitting layer that sits above the base layer but below the coat and fuzz layers. The emissive layer is tinted by the coat and fuzz, making it easy to represent emissive surfaces like a TV screen — using the coat for the reflective glass and the fuzz for dust on top.

• Coat: An optional dielectric layer that adds a secondary reflection layer over the base layer, great for clear coats and varnish.

• Fuzz: An optional layer that sits on top of everything that can be used to simulate dust or the velvety sheen of cloth.

 

In practice, working with the OpenPBR material has many similarities to Redshift's Standard material, including the set up of special effects like thin-walled diffuse transmission as seen in materials like paper and leaves. The most readily apparent differences may be seen when using the Coat Darkening effect (enabled by default) and the behavioral differences in OpenPBR's Fuzz layer vs the Standard Material's Sheen.