Mylar® OL12 (formerly known as XM963A) is a biaxially oriented polyester (OPET) film with an amorphous polyester heat seal layer. It is used as a heat sealable lidding film in packaging refrigerated and frozen foods. Mylar® OL12 is dual ovenable film which provides strong, aggressive seals to polar substrates such as amorphous polyester (APET, also PETG), semicrystalline polyester (CPET), polyester coated paperboard, and polyvinylchloride (PVC). Mylar® OL12 does not seal to polyethylene, polypropylene, or polystyrene. DuPont Teijin Films offers another family of lidding films (RL types) for sealing to these substrates. Mylar® OL12 has higher hot tack and a thicker seal layer than either Mylar® OL or OL2, and can be used in hot fill applications. It is not recommended for applications requiring retort sterilization. Mylar® OL12 lidding films have excellent grease and oil resistance. Heat seals produced with Mylar® OL12 are stronger than with Mylar® OL2 (or OL) and may be difficult to peel without shredding.