A bipolar assembly for use in electrochemical cell stacks, especially stacks operated at low pressure. The bipolar assembly is lightweight and provides a "post-type" flow field that operates with a low pressure drop. The bipolar assembly comprises a gas barrier having an array of electronically conducting posts disposed approximately perpendicular to the gas barrier. Each end of the posts is in electrical communication with the surface of an electrode. Because the bipolar assembly separates a cathode from an anode, the posts contact an anode electrode on one end and a cathode electrode on the other end. The posts provide current conduction through the stack as well as provide the flow fields for the electrochemical reactants. Optionally, the bipolar assembly may contain cooling fluid channels formed by adding additional gas barriers to the bipolar assembly. The space between the gas barriers form a channel through which cooling fluids may be circulated.