3.2. Effect of the board density on the properties of RSTIB
Thermal conductivity is the time rate of stable state heat flow through a unit area of 1 m-thick material in a direction perpendicular to the isothermal planes that is induced by a unit temperature difference across the sample [2]. The thermal conductivity, k-value,is the property of a material to conduct heat. Hence, knowledge of the thermal conductivity values allows quantitative comparison to be made between the effectiveness of different thermal insulation materials [43]. Because the RSTIB is a light-weight porous mate-rial, porosity has a significant effect on the thermal conductivity of the boards. The thermal conductivity of all boards was plotted as a linear function of boards’ density, as shown in Fig. 2. Notably, the higher density of RSTIB is associated with the higher thermal conductivity of the boards. As the board density increases, the solid substances are increased and the voids are decreased. Addition-ally, the thermal conductivity of a solid substance is much higher than that of air within the voids. This leads to a higher thermal conductivity of the whole material [35].