​Particulate materials are inherently multiphase. The solid phase includes the load-carrying granular skeleton and mobile particles. The fluid that fills the pores may be polar or non-polar, Newtonian or Maxwellian, and either singlephase or the mixture of non-miscible fluids. Fluids and viscous drag forces lead to unique phenomena in particulate materials, including the displacement of mobile particles and formation clogging, particle migration in asymmetric AC-electric fields, non unique contact angles, and the relative motion of nonmiscible permeating fluids.