Abstract: A method of heating a film prior to thermoforming by the following steps. A thermoplastic flexible film having a painted surface and a thermoplastic backing sheet is placed within a frame. The frame and film are placed within a heater. The heater has first and second radiating surfaces. The first and second radiating surfaces are parallel to the ground and the first radiating surface is above said second radiating surface. The first radiating surface is opposite the backing sheet and the second radiating surface is opposite said painted surface. The backing sheet is heated to a first temperature sufficient to cause the backing sheet to become pliable. The first temperature is a first difference above ambient temperature. The painted surface is heated to a second temperature. The second temperature is a second difference above ambient temperature and the first difference is between 2 to 20 times greater than the second difference.