The concept that the speed of preferential flow in unsaturated media may generally vary much less than the speed of matrix flow underlies a recently published model for estimating maximum preferential transport rates (Nimmo, 2007). To extend this model to predict fluxes of water and other substances requires additional information concerning the average speed of transport and the effective cross-sectional area of the flowpaths. Laminar flow theory gives relationships between maximum and average transport speeds. Various field and laboratory studies of the likely characteristics of preferential flow conduits provide information from which effective cross-sectional areas can be inferred. The model proposed here predicts fluxes of preferential flow in films that flow down the inner faces of fractures and macropores. This model includes a new characteristic function of the porous medium that is related to the medium's preferential flow capacity and in some respects to its fracture density. Various means may be feasible for estimating values of this characteristic function from field data. One such method, applied to a test case of controlled infiltration in a macroporous soil, provides estimates that show trends expected for such a soil. In a combined formulation with more conventional analysis of the nonpreferential components of flow, the new model produces reasonable predictions of water content change in response to field infiltration. This model has the advantage of predicting preferential fluxes and dynamic water contents without requiring knowledge of either discrete pathways or the unsaturated hydraulic conductivity of an equivalent medium, but rather a characteristic of the medium estimated from measurements during a single infiltration test.