An inter-laboratory comparison on thermal conductivity measurements of insulating materials is currently organized under the auspices of the Bureau International des Poids et Mesures (BIPM). Thermal conductivity measurements are carried out by seven National Metrology Institutes (NMIs) using Guarded Hot Plate apparatus according to the International Standard ISO 8302. These measurements are performed at 10 °C, 23 °C and 40 °C on resin-bonded glass fiber and expanded polystyrene boards. The same set of specimens circulates between the concerned NMIs and is thus successively measured by the participants. This international comparison is intended as a first stage (or pilot study) for future Key Comparisons between NMIs. The analysis of first results shows that the obtained values are, for any temperature, within a range of approximately ± 1.5 % (with the exception of two participants).