The fountain is especially important in the design of spouted beds for the treatment of plastic wastes. The height and structure of the fountain in shallow spouted beds have been determined by means of an optical fiber as well as by an image treatment system. The effect of the operating variables on. the fountain geometry (height and amplitude) has been analyzed by carrying out the operation with different values of the geometric factors of the contactor (base angle and gas inlet diameter) and of the operating conditions (stagnant bed height, particle diameter, particle density, particle shape, and air velocity). The materials studied are different plastic wastes (polyethylene, polypropylene, and polystyrene, both extruded and expanded). In the fountain, the core or solid ascending zone and the periphery or solid descending zone have been delimited. The experimental results prove the validity for plastic materials of the equation proven previously for prediction of the height of the fountain in cylindrical spouted beds of a conical base for glass spheres. An original equation has been proposed for prediction of the amplitude of the fountain in cylindrical spouted beds of a conical base for materials of varying density and shape.