  Using the standard fluctuational electrodynamics framework, we analytically
calculate the radiative heat current between two thin metallic layers,
separated by a vacuum gap. We analyse different contributions to the heat
current (travelling or evanescent waves, transverse electric or magnetic
polarization) and reveal the crucial qualitative role played by the dc
conductivity of the metals as compared to the speed of light. For poorly
conducting metals, the heat current may be dominated by evanescent waves even
when the separation between the layers greatly exceeds the thermal photon
wavelength, and the coupling is of electrostatic nature. For well-conducting
metals, the evanescent contribution dominates at separations smaller than the
thermal wavelength and is mainly due to magnetostatic coupling, in agreement
with earlier works on bulk metals.
