Abstract: In a method of non-destructive testing of a panel of composite insulation material (1), a portion of a surface (2) of a test panel is heated by applying a heat source for a predefined time or until a predefined amount of energy has been imparted to the panel. The heat dissipation from the surface (2) of the panel is then measured over time in order to produce a heat dissipation characteristic for the test panel, which is then compared with reference heat dissipation characteristics from panels of known composition in order to provide an initial indication of the composition of the panel. The surface (2) of the panel is then struck with a tuned hammer in order to pass a pulse of energy therethrough which generates vibrations within the panel. These vibrations are again monitored over time in order to produce a characteristic vibratory modes for the panel, which is then compared with reference data from panels of known composition in order to provide a confirmation of the composition of the test panel.