The Multi-Layer shader is similar to the, but it has a set of two specular highlight controls. The highlights are layered, letting you create complex highlights that are good for highly polished surfaces, special effects, and so on.
Upper left: No highlights
Upper right: Single highlight
Lower middle: Multiple highlights from the multi-layer shader
Highlights in the Multi-Layer shader can be anisotropic. Anisotropy measures the difference between sizes of the highlight as seen from two perpendicular directions. When anisotropy is 0, there is no difference at all. The highlight is circular, as in Blinn or Phong shading. When anisotropy is 100, the difference is at its maximum. In one direction the highlight is very sharp; in the other direction it is controlled solely by Glossiness.