A film (11) is used in a package (1) which is heated by a microwave oven to increase the internal pressure of the container, and which releases internal vapor to reduce the internal pressure. The film (11) comprises: a molecular oriented outer layer film (21); an inner layer film (23) that is laminated on the outer layer film (21) and is thermally fusible; and one or more orientation relaxation parts (21a) that are formed on the outer layer film (21) and formed by heating at a prescribed temperature or higher near the melting point of the outer layer film (21). When the tensile elastic modulus at an orientation part (21b) of the film 11 is noted as E1, and tensile elastic modulus at the orientation relaxation part (21a) of the film (11) is noted as E2, then 0<E2/E1<0.5 is satisfied.

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