This monograph systematically presents the fundamentals of theoretical and experimental research into the most important physical characteristics of porous structures. Non-standard behavior of certain physical parameters, such as the breakdown of the electric field of porous substances, is described. The method of calculation of the thermal conductivity coefficient of porous dielectrics, based on the non-equilibrium principle, is illustrated in detail. This approach is then applied to the investigation of the properties of "disparate" substances such as cellulose matrices, composites, and fibrous structures. The book is intended for physicists, physical chemists and materials scientists at research and postgraduate levels; it may also be helpful to engineers and technical workers in the applied sciences.