The optical constants of thin films of silver and titanium nitride have been obtained in the visible and near infrared spectral regions by the Nestell-Christy method. The silver films, 9-.27 nm thick, were prepared by d.c. magnetron sputtering at low pressures. It is found that the silver films, prepared at sputtering pressures below 2 mTorr, retain their bulk optical constants down to 13 nm film thickness. 5- 31 nm thick TiN films were depos-ited by reactive d.c. magnetron sputtering on 4000C heated glass substrates. The substrate heating increased the IR reflectance of the film with preserved transmittance. The free-electron character of the thin TiN films is maintained in the thickness range 13- 31 nm, as is plain from the behaviour of the optical constants. A common observation for the Ag- and TiN-films is that a low refractive index in the visible is a more sensitive criterion on film quality than the extinction coefficient. From the Drude analysis in the infrared spectral region the free-electron plasma energies and relaxation times have been derived and comparison with previous data have been made. The present results are of interest for heat-mirror development and the performance parameters for such applications are calculated and discussed.