An experimental arrangement is devised by which the absorption coefficient of low-loss materials can be measured by calorimetry using pulsed CO(2) lasers. The values obtained for long rod KCl samples are compared with those inferred when a cw CO(2) laser was used as radiation source. The values measured in the pulsed regime are little affected by the quality of the end sample surfaces and are close to the values corresponding to bulk absorption. Such behavior is explained as due to the essential role of the radiation process in dissipating the surface absorbed heat.