This work shows that the Fourier number (Fo) defines the shape and amplitude of the thermal response of a semi-infinite layer sample. The introduction of the responsivity, Rs, of the TTR method provides the ability to assess the performance of the thermal conductivity measurements. A simplified heat transfer analysis of a finite layer sample revealed that the properties ratio, (rhoC(p)K)(S)/(rhoC(p)K)(L), and the layer thickness, h/delta(P), uniquely define both temperature response and measurement responsivity. If the material under test is the substrate, this work can help improve the measurement accuracy by selecting the appropriate thickness of the top layer. If the material is a layer on top of a known substrate, this work suggests that the accuracy of the TTR measurements can be fully maximized. (C) 2004 Elsevier Ltd. All rights reserved.