Thermal conductivity of polyurethane foams

The thermal conductivity of polyurethane (PU) foams at gas pressure between 760 torr and 0.014 torr is investigated theoretically and experimentally. Six different cell sizes ranging from 150 to 350 mu m of PU foam insulation are used as the samples. Experimental results are also obtained for the spectral extinction coefficient using a Fourier transform infrared spectrometer. The thermal conductivity of PU foams for different cell sizes at 760 torr varies from 33.3 to 34.5 mW/m K, and reduces to 6.82-9.15 mW/m K at a gas pressure of 0.014 torr; the effective thermal conductivity decreases when the cell size becomes smaller. At gas pressure 0.014 torr, radiative heat transfer accounts for approximately 20% of the total heat transfer through PU foams, while solid conduction accounts for the other 80%. (C) 1999 Elsevier Science Ltd. All rights reserved.