With the development of flexible electronic technology, there is a growing demand for electrothermal materials that are environmentally friendly, safe, low-cost, and large-scale producible for efficiently solving thermal management issues. In this study, low-cost water-based carbon series electrothermal ink is prepared by a dispersion and grinding method, and the electrothermal films with various areas can be prepared on a large scale by screen printing. Simultaneously, the three-dimensional (3D) conductive network structure of graphene nanosheets (GNSs)/multiwalled carbon nanotubes (MWCNTs)/carbon black (CB) is built by the ball milling dispersion process. Due to the low percolation threshold network formed by GNSs/CNTs/CB, the prepared ink has excellent conductivity, and the square resistance (R sq ) reaches 4.3 Ω sq −1 with a thickness of 25 μm. Moreover, the saturation temperature (T s ) of the screen-printed electrothermal film (4 cm × 4 cm) can reach 165 °C with an input voltage of 10 V, and it has extremely low power consumption (444.75 cm 2 W −1 ). The electrothermal film also maintains relatively stable electrical properties in a bending test of 115 000 cycles. When the heating device (9 cm × 31 cm) is applied to the expanded polypropylene (EPP) box, the food temperature can be kept around 60 °C and the flavor can be well preserved.

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