Injection stretch blow molding is a process for manufacturing predominantly hollow objects with rotational symmetry using polymers. In this multilevel process, a preform is first produced using an injection molding process. In the next step, this preform is heated and then formed into its final shape by stretching it in all directions.

Due to the gentle heating during the blow molding process, the thermoplastic's elasticity is not very high. Effect pigments are not elastic anyway due to their inorganic composition. The stretching forms voids between the stretched polymer and the unstretchable effect pigments. The larger the pigments and the higher the stretching ratio, the more obvious the voids are. Effect pigments can be used at stretching ratios of up to 3:1. In addition, 1-level or 1.5-level processes are more suitable, because the plastic is still in a semiviscous state.

In general, this void effect is widely used to achieve the "frost effect" in PET bottles. This frost effect gives the surface an appearance like it has come directly out of the fridge.