 Subsurface scattering

Transport in which light enters a material, scatters within it and exits, potentially at another surface location. A purely local surface-reflection model does not describe all such transport.

Subsurface scattering (SSS) is a phenomenon in optics that occurs when light penetrates the surface of a translucent material, interacts with its internal structures, and then exits the material at a different location. This effect is particularly significant in materials that are not completely opaque and allow light to scatter within their volume, such as skin, wax, marble, and plants.