In a laser-driven RF gun the ultimate limit of the beam emittance is the transverse momentum of the electrons as they exit the cathode, the so-called intrinsic or thermal emittance. In this contribution we present measurements of the thermal emittance at the SwissFEL Injector Test Facility for electron beam charges down to a few tens of fC. We have studied the dependence of thermal emittance and quantum efficiency on the laser wavelength, the RF-gun gradient and the cathode material (copper and cesium telluride).