In this work, a thermodynamic model for random fields was used to study lossy materials in a reverberation chamber (RC). In particular, angular spectrum (AS) statistics were obtained inside the material and the deterministic alteration of the incidence angle at the boundary was used to find the probability density function (PDF) of the effective refraction angle. The statistical model was validated by a discrete approach and a semi-empirical model was derived to calculate the power transmitted inside a nested RC through an aperture covered by a lossy thin slab. A preliminary experimental result is presented in order to have a first check of the proposed formulation