This paper presents the thermal performance of a double-pass solar collector with and without porous media in the second or lower channel of the collector. The experimental setup has been designed to study the thermal performance over a range of design and operating conditions. Several important relationships between the design and operating conditions have been obtained. These relationships effect the thermal performance of the double-pass solar collector. The relationships include the effect of changes in upper and lower channel depth on the thermal efficiency with and without porous media. Moreover, the effects of mass flow rate, solar radiation, and temperature rises on the thermal efficiency of the double-pass solar collector have been studied. The study concluded that the presence of porous media in the second channel increases the outlet temperature, therefore increases the thermal efficiency of the systems.