To investigate the effect of PTFE coating on the breakthrough pressure, the present data for TGP 60 and the experimental data of Benziger et al. [17] for TGP 120 are plotted in Fig. 5. It can be seen that there is a direct relation between the onsets of water permeation and the PTFE loading. However, the flow threshold is not affected significantly both at low values of PTFE content, i.e., 5% Teflon coating and above 40% PTFE loading. Fig. 5, also indicates that for higher PTFE loadings, the relative drop in the breakthrough pressure drop for dried GDLs is larger. This shows that the surface PTFE coating was degraded by water flow and affected the water transport in GDL. In Fig. 6, the ratio between break through pressures at various PTFE contents, Pc, to that of the samples without PTFE treatment, Pc(0), is plotted for the present experimental data and the results reported by Benziger et al. [17]. It can be seen that both experiments follow similar trends which can be described by the following correlation: