The Sheen rollout is part of the VRayMtl parameters.
Sheen
Sheen Color – Specifies the color.
Texture – A texture map can be specified here for the sheen color.
Mix Strength – Specifies a blend amount for the texture map.
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 Sheen Glossiness example below for more information.
When the Use Roughness option is enabled, the Sheen Roughness parameter controls the amount of roughness.
Example: Sheen Glossiness
This example shows how changing the glossiness parameter of the sheen layer affects the material. The Amount is set to its default value of 1
Glossiness = 0.1
Glossiness = 0.3
Glossiness = 0.6
Glossiness = 0.8
Glossiness = 0.9
0.1
0.9