A process is provided for heat sealing substrate layers. The process comprising: conveying an upper die having a heating conductor and a lower die having a heating conductor to a sealing region, where a substrate is applied to one or more items; activating a power supply system; monitoring, via the power supply system, a temperature of the heating conductor of the upper die when in the sealing region; monitoring, via the power supply system, a temperature of the heating conductor of the lower die when in the sealing region, wherein the monitoring of the temperature of the heating conductor of the upper die is performed independently of the monitoring of the temperature of the heating conductor of the lower die; supplying power to the upper die based on the temperature of the heating conductor of the upper die; supplying power to the lower die based on the temperature of the heating conductor of the lower die, wherein the power is supplied to the lower die independently of the power being supplied to the upper die.