The Sheen tab is part of the V-Ray Mtl parameters.
Sheen
A Sheen layer can be used to create cloth materials such as satin.
Sheen color – Specifies the color.
Sheen glossiness – Controls the sharpness of reflections. A value of 1.0 means all of the light reaches the diffuse color, and when the value is smaller, the cloth material looks glossier. See the example.
Example: Sheen glossiness
This example shows how changing the glossiness parameter of the sheen layer affects the material.
Sheen glossiness = 0.1
Sheen glossiness = 0.3
Sheen glossiness = 0.6
Sheen glossiness = 0.8
Sheen glossiness = 0.9
0.1
0.9