The dependence of pressure drop in a model filter on the distance between pairs of fibers, interfiber distances in the pairs, and the orientation of the pairs of fibers relative to flow direction is calculated with allowance for the effect of gas slip along the surface of doubled nanofibers. An isolated row of doubled parallel fibers oriented normal to the flow is selected as a model filter. Flow fields in the row of the fibers and drag forces acting upon them are calculated by the Stokes equations, which are solved by the numerical method of fundamental solutions. For pairs of fibers lying in the same plane in a row, the results of the numerical calculations agree with the analytical solution.