Near solid density plasmas have been obtained by the interaction of ultraintense (2×1018 W cm−2) clean laser pulses with targets composed of different thickness of Al on a Si substrate. The depth of the x-ray emission and spectral shapes were measured using x-ray spectroscopy, which simultaneously characterized the emitting plasma and the suprathermal electron distribution. Strong modifications of the plasmas thermal radiative properties have been observed, for the first time, by changing the laser polarization from S to P. This correlates with an increase of suprathermal electrons production.