Abstract: A heat-in package with doneness indicator for heating applications, such as microwave heating of foods or sterilization applications. The doneness indicator comprises indicia printed with thermochromatic ink on the heat-in packaging. The doneness indicator can be sealed from front to back on the heat-in packaging in such a way that the heat transfer to the sealed area is controlled so that the contents contained within the heat-in packaging has adequate time to heat before a color change or other visual transformation is observed in the doneness indicator. Furthermore, the sealed area containing the thermochromatic ink is not in direct contact with the contents within the packaging. The ink changes due to heat conduction through the film. A venting system can further be incorporated to prevent excessive pressure build-up within the packaging.