Metal-polymer-metal (MPM) sheets are sandwich panels used for housings of large industrial electric motors and generators, vehicle body panels, flooring, various bulkheads, wheel arching, engine and gearbox shielding, etc. Their main advantage over classic steel panels in form of plates is their acoustic dampening properties. Joining of such plating is challenging because the polymer interlayer evaporates and the resulting fumes may cause the plates to deform. In this paper, GMAW welding was used to join metal-polymer-metal sheets, with a square butt joint, single V butt joint combined in one sheet, as well as welding in one pass per side and in multiple bead segments. C1 (CO2) and M21 (Ar + 18 % CO2) shielding gases were used. Tensile, bending and hardness tests were performed, macro and microstructures were tested and the evaporation, melting and cross-linking distances were recorded. It was shown that contrary to the recent tendency of using M21 shielding gas for GMAW welding, C1 proved to offer superior tensile and bending properties of the joint. From the point of view of simplicity and productivity, a square butt joint proved to be optimal.