A process for making an article having an irregular internal passage utilizes a hollow polymer preform. The preform is filled with a relatively incompressible filler material such as a powder or a fluid, which supports the preform when it is placed in a mold, e.g. an injection mold. The filler enables the preform to withstand high molding pressures and prevents deflection and movement of the internal passage within the preform. The shell, a layer of a polymer material is then molded about the preform. After the final article has been formed, consisting of the preform and shell, the filler is removed for possible reuse.