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 .