Abstract : Some materials, such as coffee, milk or marble, have a soft translucent aspect because of sub-surface scattering: light enters them, is scattered several times inside before leaving in a different place. A full representation of sub-surface scattering effects in illumination simulation is computationally expensive. The main difficult comes from multiple scattering events: the high number of events increases the uncertainty on the result, forcing us to allocate more time for the computations. In this paper, we show that there is a strong correlation between the surface effects of multiple scattering inside the material and the effects after just two scatter events. This knowledge will help in accelerating multiple scattering effects. We exploit this knowledge to provide a model and implementation for fast computation of double-scattering events, using a precomputed density function stored in a compact way.