Abstract: A packaging suitable for use in or on a heating appliance, comprising a bag in which, in use, is sealed an article for heating. The bag has an aperture formed therein over which is sealed a film of material which forms a window in the bag, wherein the seal between said film and the material of the bag is sensitive to temperature and/or pressure such that the window at least partially detaches automatically from the bag upon the temperature and/or pressure within the bag reaching a predefined level so as to vent the atmosphere within the bag.