Enhancing the accuracy of thermal conductivity measurements with insulating construction materials: Addressing edge effects and methodological improvements

Accurate and reliable thermal conductivity measurements are essential for evaluating the insulation properties of materials used in construction. Traditional insulating materials like glass or rock wool, or more recently developed biobased materials such as hemp wool, cellulose, flax or wood fiber panels, have very low thermal conductivity influenced by density, porosity, and temperature. However, edge effects often compromise the reliability of measurements, especially for low-conductivity materials. This study revisits the standard measurement technique with a heat flow meter proposing a refined methodology to minimize edge effects. We first show that the standard procedure based on a preliminary calibration of the heat flow meter apparatus on a reference sample to mitigate edge effects must be used with great care as it can afterwards lead to significant error on tested samples. With a model (cellulosic) material we then study systematically how the sample thickness and the temperature difference between sample and ambient air can impact measurements. In particular we show that the material anisotropy can significantly enhance edge effects, and in some cases edge effects are so large that the heat flux along one plate is negative. The analysis is completed by numerical simulations and measurements of the temperature distribution inside the sample. This work finally allows to establish the optimal thermal conductivity testing conditions for insulating materials. • Study of edge effects in thermal conductivity measurements of insulating construction materials • Optimization of conditions for accurate thermal conductivity measurements using Heat Flow Meter • Role of anisotropy in explaining thermal behavior of fibrous insulating materials