A thermal buffer tube (or pulse tube) thermally isolates two heat exchangers at different temperatures in a thermoacoustic engine or refrigerator while allowing the flow of acoustic power. For many heat transport mechanisms, the quality of the thermal isolation depends on the time-averaged mean temperature distribution in the thermal buffer tube, which is determined by boundary conditions set up by the heat exchangers. However, finite-amplitude effects within one peak-to-peak gas displacement of the heat exchangers can lead to significant modification of the thermal boundary conditions and thus the heat transport. To explore these effects, measured mean temperature profiles in the vicinity of the interface between a heat exchanger and thermal buffer tube are reported for a broad range of acoustic and thermal conditions. A one-dimensional Lagrangian model is developed to predict the mean temperature distribution, and reasonable agreement between experimental data and model results is found for the majority of the acoustic conditions considered. (c) 2005 Elsevier Ltd. All rights reserved.