Aerogel powders, particles of the group C according to the Geldart classification, are not particularly attractive as such for fluidized bed applications. The following study shows, however, that these fine solids form agglomerates above a minimum superficial velocity of 0.04 m/s and that the resulting new system fluidizes smoothly and homogeneously at room and at higher temperatures. A comprehensive model developed to represent the hydrodynamic behaviour of the system proposes that the agglomerate is a cluster of the original fixed bed materials and hence has the properties of the bulk matrix. Van der Waals forces on the elementary grains are used to predict the cluster size. This clustering process is finally analysed in the light of the classical fluidizability diagram.