PET Processing – Injection Molding. PET bottles are a huge market for the material. Processing PET into bottles can take two steps depending on the application or bottle. In the first step, PET is injection molded into a “mini bottle,” complete with threads, called a preform. This preform is then reheated, stretched and blown into its final shape. While there is technology available that combines these two processes in a single step, for larger-throughput applications preform and bottle making are generally made in distinct steps, often by different processors.