with increasing levels of force. **h** Average $\Delta R/R$ response in relation to increasing levels of force.[]{data-label="panel4"}](panel4){width="80.00000%"}

Joule heaters fabricated *via* printing nanomaterials [@Kim2013] such as graphene [@Kang2011; @Sui2011] are of great research interest. Joule heating, also known as ohmic heating is the process by which the passage of an electric current through a conductor produces heat and is currently the primary method by which many thin-film heaters function. Printed graphene heaters are have huge potential for disposable devices such as wearable heaters for therapeutic purposes [@Jang2017]. Demonstrations to date on flat surfaces has seen screen printing [@He2017] emerging as an attractive method for the large-scale fabrication of joule heaters. This is due to its ability to print thicker layers of functional materials accurately compared to other conventional printing techniques. We demonstrate the potential of our water-assisted conformal printing method to fabricate joule heaters on arbitrary substrates.

To realise joule heaters, we conformally print an unbroken spiral pattern (130 mm $\times$ 130 mm) on to a beaker and a round bottom flask; Fig. \[panel3\]a, b. The prints are allowed to dry in ambient temperature ($\sim$25 $^{\circ}$C). We then apply varying voltages of 10 V, 15 V, 25 V and 30 