modeled hair as a serial rigid multibody chain and incorporated fluid dynamics to model hair collisions and contacts. Plante et al. [2002] constrained a mass-spring system to a deformable envelope defining a volume of the cluster of hairs (wisp), which was also used for interactions. Bando et al. [2003] model the hair as a set of particles with density representing the sampled hair volume. Choe et al. [2005] combined a massspring model with a serial rigid multibody chain to model wisps, detecting contacts through cylinders. Hadap [2006] further extends the rigid multibody model to include tree structures by solving with differential algebraic equations, more easily allowing analytic constraints.