The present work aims at studying the thermophysical properties of three types of unfired earth bricks through experimental investigation, and their dynamic thermal performance (thermal capacity, decrement factor and thermal lag) as a function of wall thickness. The objective is to determine the ideal thickness of a raw earth wall, built by these bricks, to achieve the optimum values of thermal inertia. These bricks were industrially produced by the Briqueteries du Nord, which is a factory located in the north of France. The process used was the extrusion. The main difference between the three types of bricks is the origin of the soils, which were extracted from various quarries. They were characterised to determine their physical, chemical and geotechnical properties, and to identify their impact on development and production of unfired earth bricks. This work has identified the optimum thickness of the wall built by these unfired earth bricks. (It was 0.3 m for two types of bricks and for the other one was 0.4 m.) This thickness ensures the greatest heat capacity and a thermal lag between 10 and 12 hours, while taking into account the quantity of bricks necessary for the construction of such a wall and the habitable area.