Mylar® RL53T is a biaxially oriented polyester (OPET) film with an ethylene vinyl acetate (EVA) heat seal layer. It is used as a heat sealable lidding film in packaging frozen and refrigerated foods. Mylar® RL53T is designed to produce very good heat seals to a broad range of container substrates including amorphous polyester (APET, also PETG), semicrystalline polyester (CPET), polyester coated paperboard, polyvinylchloride (PVC), polyethylene (HDPE), polypropylene (PP), and polystyrene (HIPS). Mylar® RL53T has the same type heat seal layer as Mylar® RL51T, but the seal layer is thicker than both Mylar® RL51T and Mylar® RL52T. Mylar® RL53T develops stronger seals than Mylar® RL52T to most substrates. It provides the strongest seal to polystyrene containers of all RL types. Seals made with Mylar® RL53T tend to be more ductile under refrigerated or frozen conditions versus RL33 or RL43. Mylar® RL53T is recommended for applications where light caulking is needed. Mylar® RL53T has a lower seal initiation temperature than lidding films with an amorphous polyester heat seal layer (e.g., Mylar® OL, OL2). This allows good seals to be made at higher line speeds (or using lower sealing temperatures). Mylar® RL53T has corona treatment (on the opposite side of film from the heat seal layer) to enhance printing and laminating. The film is treated to an initial dyne level of 54. The dyne level of treated lidding films may decline with storage, and in-line corona treatment may be required during subsequent printing or laminating to increase the dyne level to a value adequate to get desired ink or laminate adhesion.