This work shows an experimental investigation carried out on different unfired earth building materials developed at Politecnico di Bari (Dipartimento di Architettura e Urbanistica) in collaboration with the University of Nottingham (Nottingham Centre for Geomechanics, Division of Materials, Mechanics and Structures). Several hygrothermal parameters were measured in laboratory: thermal conductivity and thermal diffusivity, water vapour permeability, water vapour resistance coefficient, sorption curves. These data were correlated with physical parameters: dry density, porosity. Furthermore some mechanical strengths were tested. The results achieved have demonstrated that the use of different clays and additives produces several changes in the microstructure, significantly influencing the thermal and hygric performances of the final products. The hygrothermal behaviour of a TESTROOM in a Mediterranean climate was also simulated by WUFI+ software. It is demonstrated that earthen materials, compared to traditional ones, show a great buffering capacity both in summer and winter. Furthermore they can contribute to achieve energy saving when HVAC system is used.