Ceramic fiber products form a class of excellent refractory insulation materials. The increasing usage of fibrous materials has given further impetus for research into their heat transfer characteristics. In order to obtain more accurate estimations of effective thermal conductivity, this paper proposes a numerical model with a random structure to estimate the effective thermal conductivity of ceramic fiberboard under various bulk densities and temperatures. The present model is able to sort out individual contributions of conduction and radiation heat transfer mechanisms in these materials. The numerical simulation results are in good agreement with measured values obtained by a guarded hot plate (GHP) apparatus, indicating that the adopted modeling approach can be extended to other insulation systems.In recent years, energy saving and emission reduction have remained very difficult tasks. To meet the requirements of the current energy situation, insulating media have been increasingly used. The most widely used categories of insulating materials are inorganic fibrous and organic foamy products. Organic foamy materials cannot be used in high temperature conditions, due to their poor resistance to high temperatures and the increased hazards in case of fire. As a result, only fibrous materials are considered in this paper. Among the fibrous materials, ceramic fiberboards have received special attention due to their excellent properties, such as light weight, high temperature resistance, low thermal capacity, good heat insulation performance, nontoxicity, etc. Because of these merits, ceramic fiberboard can not only be used as thermal and acoustic insulation but also for fire protection. The thermal performance of ceramic fiberboard is based on the air trapped between fibers, resulting in its low thermal conductivity. Therefore, ceramic fiberboard is better than insulation brick and other traditional refractories in energy saving, which means it has been widely used in various fields.The increasing usage of fibrous materials has given further impetus for research into their heat transfer characteristics. Early studies reported the relative magnitudes of the different modes of heat transfer in planar fibrous materials. 1-3 Many investigations have focused on the behavior and modeling of heat transfer in fibrous materials, for example, radiative heat transfer through porous insulations, 4 radiation properties in fibrous insulations, 5-7 semi-empirical modeling of heat transfer in dry mineral fiber insulations, 8 heat and mass transfer in fibrous insulations, 9 numerical modeling of radiative transfer in fibrous media, 10 approximate formulation for coupled conduction and radiation through a medium with arbitrary optical thickness, 11 and combined radiation and conduction heat transfer in high temperature fiber thermal insulation. 12 More recently, a number of investigations have been carried out for modeling heat transfer in fibrous materials. [13][14][15][16][17][18][19] However, most of the reported methods are onl...