Results are presented from a study of the changes in characteristics of the pore structure, gas permeability, and mechanical properties of materials UPA-3 and UPA-4, which are based on knitted and fabric fillers. The textiles of the materials have different structures and are based on carbon fibers (which are obtained using oxidized polyacrylonitrile and different grades of viscose). The changes in the characteristics are examined in relation to the degree of pre-compression of the materials and the length of time that they undergo compaction with pyrolytic carbon and graphite.