On Sept. 10, 2007, the Cassini spacecraft encountered Saturn's third largest moon, Iapetus, during the closest encounter with the two-toned moon to date. During this experiment (called the IA49-3 experiment), the Cassini radar/radiometer observed the leading hemisphere of the moon, collecting a unique passive (radiometry) and active (radar) data set at the wavelength of 2.2-cm. At such a wavelength, the radiometer probes several tens of cm up to a few meters below the surface, depending on the absorbing properties of the regolith. In this paper, we show that the seasonal contrast between the high latitude terrains of Iapetus was captured during IA49-3 thus providing new constrains on the electrical and thermal properties of the moon's surface.