This paper presents a structural model of complex materials that are partly or entirely of cellular structure, and a new model of thermodynamics, which can be applied to the processes taking place in complex materials. Since the complex materials always contain cellular fraction, the supposition of cellular equilibrium is real. The complex materials are characterized by polyagent behaviour. Therefore, new concepts such as principal variables, redundancy, macroscopic/microscopic uncertainty are defi ned, moreover, the application of chemical thermodynamics is limited to micro processes only, and the free energy (F) and the free enthalpy (G) function cannot be generally applied to calculations concerning the bulk amount. Temperature as only a local intensive variable can be discussed. The fi rst law of thermodynamics is expressed in the traditional way. The second law applied to the processes taking place both in open and in adiabatically closed systems is formulated as in words as an equation of stability, completed by the relations to fi rst and second differential of entropy. In connection with the second law the Damköhler balance equation system, the Rabinowitsch-Mooney equation, and the application of dimensional analysis are presented. Only the apparent thermal capacities can be used for complex materials in general. The data of specifi c thermal capacity of complex materials in the proximity of absolute zero temperature are not suffi cient for drawing conclusions on their entropy. The concept 'shelf-life' is essential in food science and practice, a Monte-Carlo method is presented for its calculation.