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 ofthe thermal conductivity values allows quantitative comparison tobe made between the effectiveness of different thermal insulationmaterials [43]. Because the RSTIB is a light-weight porous mate-rial, porosity has a significant effect on the thermal conductivity ofthe boards. The thermal conductivity of all boards was plotted as alinear function of boards’ density, as shown in Fig. 2. Notably, thehigher density of RSTIB is associated with the higher thermal con-ductivity of the boards. As the board density increases, the solidsubstances are increased and the voids are decreased. Addition-ally, the thermal conductivity of a solid substance is much higherthan that of air within the voids. This leads to a higher thermalconductivity of the whole material [35].The board density affects the IB and