A PVDF-based PNG (28 μm 5.0 cm 9.4 cm) was holdabove a heat source for the performance test (Figure 2a).Since the PNG was very thin and flexible, it was hard to useconventional thermometers to measure its temperature insitu and in real time. Taking advantage of a high-tech IRcamera, we was able to measure the in-situ and real-timetemperature map of the PNG under different experimentconditions (Figure 2b–e). Continuous hot water vapor wasgenerated by heating a wet towel. As a contrast, we used adry towel replacing the wet towel, where only air and IRradiation was available for heat transfer. We also varied thedistance between the PNG and the towel, to study thetemperature oscillation behavior of the PNG. The combination of two heat transfer agents (water vapor or air) and twodistances between the PNG and the heat source (3.5 cm or7.0 cm) gave four different experiment conditions.