A durably expandable microwave interactive insulating material comprising: a microwave energy interactive material supported on a first polymer film layer, the microwave energy interactive material being operative for generating heat in response to microwave energy; a second polymer film layer joined to the microwave energy interactive material in a patterned configuration, thereby forming at least one closed cell between the microwave energy interactive material and the second polymer film layer, wherein at least one of the first polymer film and the second polymer film comprises a barrier material adapted to maintain the closed cell in an inflated condition after exposure to microwave energy has ceased; and a gas-releasing reagent disposed on at least a portion of at least one of the microwave energy interactive material and the second polymer film layer adjacent to the at least one closed cell, the gas-releasing reagent being operative for releasing a non-water vapor gas in response to heat from the microwave energy interactive material to inflate the closed cell, characterized in that the microwave energy interactive material and the second polymer film layer are joined directly to one another, such that there is no layer of paper between the microwave energy interactive material and the second polymer film layer, and such that the gas-releasing reagent is not bound within a layer of paper, and the gas-releasing reagent comprises at least one of (a) a blowing agent, and (b) two or more substances that react with one another to produce the gas. a microwave energy interactive material supported on a first polymer film layer, the microwave energy interactive material being operative for generating heat in response to microwave energy; a second polymer film layer joined to the microwave energy interactive material in a patterned configuration, thereby forming at least one closed cell between the microwave energy interactive material and the second polymer film layer, wherein at least one of the first polymer film and the second polymer film comprises a barrier material adapted to maintain the closed cell in an inflated condition after exposure to microwave energy has ceased; and a gas-releasing reagent disposed on at least a portion of at least one of the microwave energy interactive material and the second polymer film layer adjacent to the at least one closed cell, the gas-releasing reagent being operative for releasing a non-water vapor gas in response to heat from the microwave energy interactive material to inflate the closed cell, characterized in that the microwave energy interactive material and the second polymer film layer are joined directly to one another, such that there is no layer of paper between the microwave energy interactive material and the second polymer film layer, and such that the gas-releasing reagent is not bound within a layer of paper, and the microwave energy interactive material and the second polymer film layer are joined directly to one another, such that there is no layer of paper between the microwave energy interactive material and the second polymer film layer, and such that the gas-releasing reagent is not bound within a layer of paper, and the gas-releasing reagent comprises at least one of (a) a blowing agent, and (b) two or more substances that react with one another to produce the gas. (a) a blowing agent, and (b) two or more substances that react with one another to produce the gas.