PET bottles are the shooting stars of the packaging industry, and the importance of polyethylene phthalate (PET) for a wide variety of applications continues to increase steadily. As PET is used more and more in the packaging industry, the possibilities of shapes and sizes have expanded. Increasingly, PET packaging is encountered not only in the form of bottles for soft drinks, but also for applications that include containers for soaps, cosmetics, cleaners, pharmaceutical products, or commercial bulk products. In contrast to PET, there are decades of experiential values available for glass. Furthermore, glass presents few if any problems with regard to its material properties (mechanical and chemical stability, light sensitivity), also with respect to oxygen diffusion. Simply stated, pure PET is transparent to practically the entire solar light spectrum. In other words, a PET package is not only transparent in the visible range of the spectrum, but both UV and thermal radiation pass through the plastic practically unhindered to strike the underlying contents.