Thermal/infrared non-destructive testing (T/I NDT) appeared in the 1970s as a mainly experimental technique. In its active implementation, T/I NDT is inherently related to some methods and technical means of thermal stimulation, such as optical, convective, eddy current, microwave and ultrasonic heating. Therefore, the mechanism of defect detection in T/I NDT is governed by heat conduction laws. The paper contains the analysis of analytical and numerical solutions to typical T/I NDT models where defective materials are subject to thermal stimulation. The comparison between 1D, 2D and 3D models is presented to illustrate the accuracy of particular solutions. Both 'classical' and advanced models are comparatively studied to illustrate the influence of material anisotropy and optical semi-transparency, as well as some other factors, on observed temperature signals. (C) 2014 Elsevier Ltd. All rights reserved.