Fig. showed that the proton conductivity of the ZrP membrane is 3.4 mS cm -1 at 80°C and 95%RH. The conductivity of the ZrP crystal itself is known to be about 0.3 mS cm -1 at 90°C and 90%RH from a previous study, and it is also known that the conductivity of various ZrP-PTFE films is about 0.1~10 mS cm -1 , , . In addition, considering that the porosity of the substrate used in this study is 55% (pore size: 30 nm), the conductivity of the ZrP membrane is sufficiently high. It may be due to the effect of the counter-ions on the surface of ZrP crystals, as described in 4.1. Furthermore, the thickness of the membrane synthesized in this study is 7~10 μm, which is beneficial because the resistance of the membranes in PEMFC is reduced by making PEMs thinner . The thickness of the Nafion® film is about 50-150 µm, and that of most of the PEMs reported so far is about 50 µm thick , . It is because if a film becomes thinner, its strength cannot be sufficiently maintained, and at the same time, fuel permeation is likely to occur. On the other hand, the membrane synthesized in this study is durable because of the strong PE backbone and the high ZrP content in relatively small pores (less than 30 nm), which should reduce fuel permeation.