Mylar® RL43T is a biaxially oriented polyester (OPET) film with an ethylene vinyl acetate (EVA) heat seal layer. Mylar® RL43T is designed to produce strong heat seals to polypropylene (PP). Although designed especially to seal to polypropylene, Mylar® RL43 will produce strong seals to a broad range of container substrates including amorphous polyester (APET, also PETG), semicrystalline polyester (CPET), polyester coated paperboard, polyvinylchloride (PVC), polyethylene (HDPE), and polystyrene (HIPS). Mylar® RL43T has the same type heat seal layer as Mylar® RL42T, but the seal layer is thicker than Mylar® RL42T. Mylar® RL43T produces the highest seal strengths to polypropylene of Mylar® lidding films and tends to produce tearing seals to non-polar substrates under chilled conditions. Mylar® RL43T is recommended when light caulking is needed. Mylar® RL43T, like other RL types, 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® RL43T has corona treatment (on the opposite side of film from the heat seal layer) to enhance printing and laminating. This film type is marketed by DuPont Teijin Films as Mylar® RL43T. 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.