Thermal shock damage has been investigated in a WC-7 wt.%Co hardmetal and in a TiMoCN-26 wt.%Ni cermet by measuring their loss of bending strength after repeated quenching in water. The behavior of the hardmetal is significantly better than that of the cermet, showing a less abrupt loss of strength as quenching temperature step increases. Experimental values are in good agreement with R parameter predictions, especially for the cermet. Biot numbers are low enough to neglect the effect of transient heat transfer phenomena. It is concluded that a low thermal expansion coefficient combined with high strength and toughness are critical parameters to ensure an optimum thermal shock resistance.