alSurface

A physically plausible, energy-conserving, general-purpose surface shader.

Diffuse
The diffuse layer sits underneath both specular layers and so its intensity is scaled according to the Fresnel transmission of both the specular lobes.

Backlight

The backlight layer represents light that is diffusely transmitted from the reverse side of the object and it useful as a cheap subsurface effect for thin ojects such as cloth, paper and leaves. It sits underneath both specular layers and so its intensity is scaled according to the Fresnel transmission of both the specular lobes.

SSS

The Subsurface scattering layer represents light that has entered the material and been scattered and absorbed such that it diffuses through the material. The SSS lobe has 3 layers that can be used to define a more complex shape to the scattering falloff, and can be thought of like layers within a more complex scattering material such as skin. The weights of the individual layers are normalized before use, and the order of them does not matter. The SSS lobe underneath both specular layers and so its intensity is scaled according to the Fresnel transmission of both the specular lobes.

Advanced

The Advanced section contains controls that allow you to fine-tune the behavior of the shader. You should not need to touch these under normal circumstances.
Specular 1
Specular (glossy) layers represent light that is reflected immediately at the boundary of the surface. The specular 1 lobe sits on top of all the others and so both receives all the light and attenuates the light reaching all other lobes. It can be used either as the primary specular for the material, or as a clear coat layer on top.

Fresnel

Fresnel controls how much light is reflected the the specular lobe (and at what wavelengths) depending on the angle at which the light hits the surface.

Advanced

The Advanced section contains controls that allow you to fine-tune the behavior of the shader. You should not need to touch these under normal circumstances.
Specular 2
Specular (glossy) layers represent light that is reflected immediately at the boundary of the surface. The specular 2 lobe sits underneath the specular 1 lobe and so is attenuated by it and attenuates the light reaching all other lobes. It can be used either as the primary specular for the material, or as a clear coat layer on top.

Fresnel

Fresnel controls how much light is reflected the the specular lobe (and at what wavelengths) depending on the angle at which the light hits the surface.

Advanced

The Advanced section contains controls that allow you to fine-tune the behavior of the shader. You should not need to touch these under normal circumstances.
Transmission
The transmission lobe describes light that is refracted through the surface. It allows you to create materials such as water and glass.The transmission lobe sits underneath the two specular layers and is attenuated by both. Any changes that affect the color of the transmission lobe, such as Color or the Attenuation controls, will also color the object's shadows.

Attenuation

The attenution parameters allow you to control how light is absorbed and scattered as it travels through the inside volume of your surface in order to simulate effects such as smoked glass, absorption through water etc. By default, only absorption is calculated, while setting Scattering to some value greater than 0 will calculate (single) in-scattering as well.

Advanced

None
Emission
The emission lobe represents light that is emitted from the surface itself. It sits beneath the two specular lobes and so is attenuated by both of them.
IDs
Whatever you plug in or set in the ID parameters in this section is written straight out to the corresponding id_X AOV. This is exteremely useful for creating mattes, or for outputting textures or other sub-network results to be used in comp.
AOVs
Use these parameters to change the name of the AOVs that the shader writes
Advanced
The Advanced section contains controls that allow you to fine-tune the behavior of the shader. You should not need to touch these under normal circumstances.