OptionalsheenLinear RGB sheen reflectance in [0, 1] per channel; defaults to [0, 0, 0].
OptionalsheensRGB RGB texture multiplied by sheenColorFactor; alpha is unused.
OptionalsheenUnitless perceptual sheen roughness in [0, 1]; defaults to 0.
OptionalsheenLinear alpha-channel texture multiplied by sheenRoughnessFactor; RGB is unused.
Ratified Khronos cloth sheen extension, KHR_materials_sheen.