The development of coatings which show a good thermal conductivity plays an important role in the realization of new laser schemes like the Yb:YAG disk laser. We present results on investigations on the thermal conductivity of different thin film materials produced by conventional thermal evaporation and ion beam sputtering. With the optimized IBS-process high reflecting coatings are produced on the end faces of Yb:YAG disk lasers. A significant reduction of the thermal gradient in the laser disk was observed, which is an essential requirement for high power lasers besides the excellent optical quality of the coating.