The separator is a critical component for the performance of alkaline water electrolysis as it ensures the ionic contact between the electrodes and prevents the product gases from mixing. While the ionic conductivity of the separator affects the cell voltage, the permeability of the dissolved product gases influences the product gas impurity. Currently, diaphragms are used as separators, the pore system of which is filled with the electrolyte solution to enable the exchange of ions. The breakthrough of the gas phase can be prevented up to a specific differential pressure. A drawback of diaphragms is the requirement of a highly concentrated electrolyte solution to maintain a high ionic conductivity. The usage of anion-exchange membranes could solve this problem. However, the long-term stability of such materials remains unproven. This study compares two pre-commercial diaphragms, an anion-exchange membrane, and an ion-solvating membrane with the state-of-the-art diaphragm Zirfon^TM Perl UTP 500. Besides physical characterization, the material samples were evaluated electrochemically to determine the ohmic resistance and the product gas impurities. The results show that the thinner diaphragm outperforms the reference material and that polymer membranes can compete with the performance of the reference material.