Abstract: In this paper we present a technique for simulating and rendering liquid foams. We are aiming at a functional realism that allows our simulation to be consistent with the physical effects in real liquid foam while avoiding the prohibitive computational cost of a physically accurate simulation. To this end, we have to recreate two important attributes of foam. The dynamic behaviour of the simulated foam must be based on the physics of real foam, and the characteristic interior structures of foam and their optical properties must be reproduced. We tackle these requirements by introducing a two part hybrid rendering approach. The first stage is geometric and determines the dynamic behaviour of the foam by simulating structural forces on a set of spheres, which represent the foam bubbles. In the second stage we render these spheres using a special surface shader that implicitly reconstructs the foam surfaces and performs the shading calculations. This two step approach allows us to easily integrate our technique into existing ray-tracing systems. We include images of an example animation to demonstrate the visual quality.