If you think in terms of PBR rendering: * refractive index determines the split between reflected and refracted light vs angles. * diffuse albedo determines t

If you think in terms of PBR rendering: * refractive index determines the split between reflected and refracted light vs angles. * diffuse albedo determines the absorption of refracted light. * specular albedo determines the absorption of reflected light. * opacity determines the scattering of refracted light. * roughness determines the scattering of reflected light. In PBR, metals are modeled with a purely black diffuse albedo (with very high refractive index), while dielectrics are modeled with a purely white specular albedo. A transparent dielectric means all the refracted light goes straight, while a opaque white dielectric means all the refracted light are scattered (but not absorbed!) For metals, it doesn't really matter whether the refracted light is scattered or not, if they're all gonna be absorbed anyways. --- EDIT: laying out the parameters like this, I just realized why Unreal Engine's PBR felt "off" at times -- their "metalness" workflow does not allow you to adjust the refractive index of metals! I'm guessing they just assume that metals have infinite refractive index and so the refraction-reflection split is 0%-100% with no angle dependence. This means that they are generally overestimating how shiny metals should look with no Fresnel effect at all.