Abstract
Polymeric foams are one of the most efficient thermal insulation materials because of the extra low thermal conductivity blowing agent gases trapped inside of the closed porous structures. Thermal conductivity is one of the most exclusive properties of foamed polyisocyanurate (PIR) materials. The blowing agent gases are selected based upon their characteristics of low thermal conductivity and slow diffusion rates through the foam polymers. The atmospheric gases have a greater thermal conductivity and are typically much smaller molecules with much faster diffusion rates through the foam. PIR gains much of its thermal resistance value from the blowing agents, often a pentane gas mixture, which is trapped in the foam cells. Pentane isomers are commonly used in Europe in manufacturing rigid insulating polyurethane foams. Since the thermal conductivities of the pentanes (between 0.010 and 0.014 W/(m⋅K)) fall significantly below that of air, polyurethane insulation panels may achieve thermal conductivity as low as 0.024 W/(m⋅K). This paper analyses results of the thermal conductivity study and measurements according to two different parameters: the initial value of thermal conductivity and the rate of aging, i.e., the rate of increase in thermal conductivity over time. The initial thermal conductivity value is influenced by the thermal conductivity of the gas inside the cell and the average diameter of the cell.