A container is provided that has a compartment for storing an air-activated material for heating contents. The compartment is formed between a first web of material and a second web of material. The first web includes a first film layer laminated to a second film layer. A portion of the first film layer of the first web can be separated from the second film layer to reveal openings in the first film layer that allow air to enter the compartment. When the air contacts the air-activated material to activate the material, an exothermic reaction takes place that serves to produce heat, such as to heat the contents of the container. Prior to separation of the first and second film layers, the container is designed to allow ingress of oxygen into the compartment at a rate less than approximately 3 cc per 100 in2 per 24 hrs. at 23° C.