Poly(ethylene terephthalate) (PET) is widely utilized for the production of food and beverage containers as it has low permeability to water and carbon dioxide. As with other semi-crystalline thermoplastic polymers, the physical and mechanical properties of PET depends on the degree and quality of crystallization. The amount of crystallization or percent crystallinity depends on the micro structure and how fast the liquid polymer is cooled during solidification. According to ISO11357-3, DSC can be used to study thermal transitions such as melting, crystallization and glass transition of polymers. This application news examines the crystallinity properties when the liquid PET is cooled at different rates using a differential scanning calorimeter (DSC).