Fractional penetration through four fibrous filters was determined experimentally at various air velocities. To describe the data obtained for multilayer sets of filters composed of up to nine layers of the same filter, the axial dispersion model was applied. This model predicts a non-exponential decrease of aerosol penetration with a filter thickness increase. The dispersion model contains two parameters, λ and Dx, which were evaluated on the basis of the experimental data. For the first time ever the axial dispersion coefficients, Dx, in fibrous filters were determined.