The thickness and inner structure of porous fibrous structures - textiles is an important parameter, especially regarding comfort, noise, heat insulation, and permeability. The standard and probably the fastest thickness measuring method is with a thickness gauge, which uses a certain slight pressure, as well as other known methodologies. The paper presents an original methodology for evaluating the thickness of non-pressure-controlled porosity structures using their transversal packing density distribution. It also determines the maximum packing density value of the evaluated structure and the packing density level at which the thickness gauge approximately measures the thickness. The ratio of pressure-controlled and non-pressure-controlled thicknesses is used to define the proportion of the “incompressible” core of the fabric to its “compressible” surface. The packing density is evaluated in transverse virtual cross-sections of the structures using an image analysis tool. The standard soft cross-sections that are used could again cause some deformation of the studied structures, so the cross-sections were performed using Rigaku’s nano3DX computed tomography equipment. The methodology was tested on a set of seven diverse textile structures in terms of material and manufacturing technology. Each test specimen was evaluated for its internal structure through the transverse packing density process, the corresponding mentioned packing density levels were found, the non-pressure controlled thickness was determined, and the core and outlying fibers ratio was defined. The maximum packing density in the fabric core decreased as expected from the woven fabric through the weft and warp knitted fabric to the non-woven fabric. The maximum transverse packing density is independent of the thickness and the material used and, therefore, depends only on the structure. So is the packing density level at which the thickness gauge measures the thickness. This level has been set at 0.028 for knitted fabrics.
