Alkaline water electrolyzers are traditionally operated at low current densities, due to high internal ohmic resistance. Modern diaphragms with low internal resistance such as the Zirfon diaphragm combined with a zero gap configuration potentially open the way to operation at higher current densities. Data for the Zirfon diaphragm show that the resistance is only 0.1–0.15 Ω cm2 in 30% KOH at 80 °C, in line with estimations based on the porosity. Nevertheless, an analysis of data on zero gap alkaline electrolyzers with Zirfon reveals that the area resistances are significantly higher, ranging from 0.23 to 0.76 Ω cm2. A numerical simulation of the secondary current distribution in the zero gap configuration shows that an uneven current distribution, imperfect zero gap and the presence of bubbles can probably only partly explain the increased resistance. Therefore, other factors such as the presence of nanobubbles could play a role.