Researchers derived a mathematical model of filtration to calculate the hydraulic resistance of a layer of unattached fibrous or nonwoven material when deformed by filtration flow. The Darcy filtration equation, which expressed filtration flow rate, permeability coefficient, differential pressure gradient of the filtration flow, and viscosity, was used in these calculations. The permeability coefficient derived from the Carman-Kozeny equation, which expressed the porosity of the fibrous material, its specific surface area, and the Kozeny constant. Analysis of the permeability of different textile materials in air showed that the relationship between permeability and pressure culd be described by a power function, with the exponent n for most materials equal to 1.5. However, based on studies of filtration of polymeric solutions through layers of finely cut fiber, the researchers showed that n culd also vary within wide limits. In steady state liquid filtration, values of n ranged from 1.5 to 1.8, and attained 3.3 when the permeability of the fiber membrane changed cue to metamorphosis of the pore structure. The mathematical model accurately predicted many critical conditions of liquid filtration, such as maximum acceptable flow rate, maximum filling density, and the layer height of fibrous media with known compressability parameters. 4 refs.