The following documentation is based on images created by the Khronos Group.
Overview
A PBR material defines different parameters and textures that influence its aspect in a global or local scale. The PBR is the result of the combinaison of these parameters and textures.
Water bottle designed with a PBR material using 6 different textures.
Parameters
base color
The color of the material is independent of the lighting conditions. It is the diffused albedo for a non-metallic material and the specular color for a metallic material.
The alpha value of the color represents the opacity of the material.
Texture is made of flat colors without any light effect.
metalness
The value represents how much the surface covered by the material appears metallic.
The metalness may be defined at a global level with a factor and at a local level with a texture that can finely define the value over the covered surfaces. Both components can be used to combine their effects.
Texture describes the metallic areas (white) and the others (bottle cap and rubber sleeve in black).
roughness
The value represents how much the surface covered by the material is smooth or rough.
The roughness may be defined at a global level with a factor and at a local level with a texture that can finely define the value over the covered surfaces. Both components can be used to combine their effects.
Rubber sleeve is rougher (light gray) than the metallic bottle and its cap (middle gray).
normal map
A texture that simulates the bumpiness on a surface. It enables to simulate details on a surface without the need to create their geometry.
Details (incrusted logos, text...) are added without need of geometry.
occlusion map
A texture that defines how much the ambient light affects a point on a surface. It is used to represent the influence of close geometries that decrease the lighting received by their surfaces.
Areas between elements (bottle, cap, rubber sleeve) are lightly occluded.
emissivity
A color that represents the light emitted by the surface like a neon for instance. As it is not a true source of light it will not affect other surfaces.
Texture fakes the light of a digit screen giving time and temperature.
opacity
A value that describes how a transparent surface covered by the material is mixed with the surrounding environment.
The material can be defined as opaque, blended or used as a mask.
When opaque, the surfaces always hide what's behind.
When blended, the surfaces show the environment through.
When used as mask, the local areas of the surfaces show or hide according the local opacity value.
The bottle is fully opaque.
culling
A value that represents which side of a surface is visible. Essentially used whether to render both sides in the case of transparent geometries or the interior of volumes seen through holes.
The bottle requires standard culling as there is no transparent areas.