Mylar® RL53 (formerly known as XM340) 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® RL53 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® RL53 has the same type heat seal layer as Mylar® RL51, but the seal layer is thicker than both Mylar® RL51 and Mylar® RL52. Mylar® RL53 develops stronger seals than Mylar® RL52 to most substrates. It provides the strongest seal to polystyrene containers of all RL types. Seals made with Mylar® RL53 tend to be more ductile under refrigerated or frozen conditions versus RL33 or RL43. Mylar® RL53 is recommended for applications where light caulking is needed. Mylar® RL53 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).