This paper reviews the basic mechanisms of heat transfer, namely conduction, free convection, and radiation in fibrous insulations. The relative contributions of these phenomena to the effective or the overall thermal conductivity of fibreglass insulation are assessed. The Rayleigh number calculations show that free convection effects may generally be ignored, especially for horizontal layers. Statistical bounds for the combined fiber and gaseous thermal conduction are discussed for different orientations of the fibres. The procedure for calculation radiation conductivity through a solution of Maxwell's equations is discussed and illustrative results are presented. Calculated results for the effective conductivity for commonly used density and temperature ranges are discussed.
