The diffuse parameters control the look of basic diffuse reflection. These are often used to define primary color attributes for opaque objects; wood textures, label text, polka dots, or more, you can find them all connected here.
Gain is the weight applied to the diffuse parameters. You may also drive this with another pattern to show things like fading or wetness (where liquid darkens a surface). Below are examples at 0.0, 0.5, and 1.0 gain for a 50% grey material.
Color is typically where textures or patterns are connected to create color for opaque objects. This is where a wood color texture would go, for example.
Diffuse roughness is how you would simulate a powdery surface like dried clay or dust.
Bump mapping is a great way to fake the appearance of physical detail using shading instead. If this is not set, it will use the global bump normal specified in the Properties section near the bottom of this page.
If on, illuminate both sides of the surface for this diffuse lobe, that is, this will illuminate the surface whose normal is pointing away from the camera (2-dimensional objects) as well.
The specular parameters control speculal reflection. This is where you might define how shiny or reflective an object is. Is it plastic, a polished marble table, or is it a mirror?
Select which specular model to use: Beckmann or Ggx. Ggx may be preferred here for its "tail", or how the highlight has a soft fade from the center reflection of a lightsource.
Specular color at facing angle (0 degree incidence). Note that there is no separate gain control. To control the specular "gain", simply adjust the color value or connect it to a PxrExposure node.
Specular color at the glancing angle (90 degree incidence). To control the edge specular "gain", simply adjust the color value or connect it to a PxrExposure node.
Specular fresnel curve exponent. Lower numbers reduces the effect of Face Color while increasing the effect of Edge Color. Higher numbers reverse this. If your face and edge colors are the same, then there is no visible effect.
Specular roughness. A greater value produces rougher or "blurry" specular reflection. At 1.0 it resembles a diffuse surface and at 0.0 it's a perfectly clear reflection. Most objects will be realistic somewhere in between these values. Texturing this value may give you interesting effects like smudges, greasy fingerprints, and worn surfaces.
Controls the shape of the specular highlights and reflections. 0 means isotropy which produces the regular circular specular highlight. Values from -1.0 to 1.0 produce the range of ellipses (stretching) from wide to tall.
By default, the direction of anisotropy is controlled by the model texture parameters. If the Shading Tangent is specified, it is used instead.
Controls the anisotropy direction. Only valid when it is connected to a pattern. This is useful for making brushed metals.
Normal to use for the specular illumination. If this is not set, it will use the global bump normal specified in the Properties near the bottom of this page.
If on, illuminate on both sides of the surface for this specular lobe, that is, this will illuminate the surface whose normal is pointing away from the camera as well.
Similar to Specular parameters except it has a larger default roughness which is 0.6. This layer is intended for use with higher roughness settings than the Specular lobe above.