A disposable cover for an infrared thermometer provides IR window isolation of handling and usage generated forces. The cover comprises a thin sidewall linked to the film window with a collar structure. The collar structure includes one or more characteristics that either isolate the film window from externally applied forces, or develops counter forces in a way that precludes film stretching and other transmission distorting effects. In a preferred embodiment, the probe includes retention ears and the cover includes a rim that cooperatively engages the retention ears. This combination of retention ears and an interlocking rim decreases movement of the cover along the probe axis. The cover of the present invention permits sanitary application of an infrared clinical thermometer without hindering reading accuracy or patient comfort.