sheen_film.shader

A metallic-roughness surface carrying two lobes the standard material does not: a sheen lobe for fabric, and thin-film iridescence.

sheen scales the lobe, sheen_color tints it and sheen_roughness sets its width — a low roughness gives satin's tight rim, a high one velvet's broad glow.

iridescence blends toward the thin-film response, iridescence_thickness (in nanometres) sets which wavelengths interfere and so which hues appear, and iridescence_ior sets how strongly the film refracts.

Both are off at their defaults, and both are evaluated by the engine's light loop, so they are shadowed and lit like any other surface.