This paper proposes a procedure for the numerical evaluation of the efficiency of countermeasures in the thermal infrared. This procedure consists of three phases. In the first phase, the characteristics of different thermal camouflage materials are tested on a lab-scale. These tests comprise measurements of the attenuation of the incident infrared energy and/or of the thermal emissivity factor. With respect to the attenuation measurement, a calibrated infrared sensor is used to determine the radiation patterns of an object. The comparison of these patterns before and after the application of a camouflage system gives an absolute measure of its attenuation. The result of this measurement is important since the attenuation is closely related to the contrast between the camouflaged object and its background and thus to the probability of detection. Contrast, however, is not the only important feature for the detection of an object in a thermal image. That is why in a second phase the countermeasures under evaluation are tested in a real environment. During this phase, a numerical value is given to the efficiency of the considered camouflage in the thermal infrared, using features selected from those which are known to be important for human vision. These include, besides contrast, other features such as correlation and texture. The third and final phase aims at a verification and a validation of the test results. Indeed, it is of a crucial importance to find a link between the performances obtained in the field and the characteristics measured on a lab- scale. It is also necessary to verify that a good correlation exists between the efficiency as determined by human observers or by numerical evaluation. This is now taking place using a database of thermal images taken with a GEC Avionics TICM II (8 to 12 micrometers ). Those images are then presented to human observers and to the machine in a project called Psychotest.