A theoretical description of single-phase flow through porous media having permeable boundaries is presented. The volume averaged momentum transfer equation is solved numerically by a finite difference technique after neglecting the nonlinear inertia term. The influence of fluid slip on axial velocity profiles and wall skin friction is analyzed as a function of cross-flow and the porous medium shape factor. Boundary effects on momentum transfer are quantified. The implications for the design of scale models for porous media such as filters, adsorber columns, and aeration towers are discussed. In accordance with experimental data obtained by other researchers, it is shown that in most cases, additional viscous dissipation effects due to the presence of boundaries are expected to be insignificant even in laboratory-scale models only a few packing element diameters wide.