A theory is presented to describe the relationship between the structure ofasheetofpaperandtheflowoffluidsthroughit.Basedonthemultiplanarconcept of paper, it defines a pore through the sheet in terms of structural and hydrodynamic variables. The effective pore size distribution thus depends on the type of flow,as well as on the structure of the sheet. It is in all cases approximately lognormal, with a standard deviation proportional to the mean.
The theory is applied to the problem of the maximum pore size and to laminar flow, for which the connection with the Kozeny-Carman equation is established.
The theory correctly predicts relationships between physical and structural variables and fibre/sheet properties. Numerical agreement with experiments is still limited by the lack of an appropriate definition of a layer in the multi-planar model.