<p>We carried out non-contact measurements of thermal diffusivity in air using the Angström method with an infrared camera, specifically for small samples to which temperature sensors cannot be attached. Thermal diffusivities of an alumina plate, a skutterudite plate, a glass fiber, and a silk fiber were successfully measured, and the influence of heat loss on the measurements was investigated. In the analysis, a model assuming a constant heat transfer coefficient to the air was employed, and the validity of the method was confirmed by comparing the measured values with literature data. The limitations of the constant heat transfer coefficient model under unsteady state conditions were also clarified. The results show that the present heat-loss model is sufficient for practical measurements of thermal diffusivity in air. Furthermore, this approach enables a quantitative assessment of whether vacuum conditions are necessary for accurate measurements.</p>