The performance of three integrated micro packed bed reactor-heat exchangers (IMPBRHEs) for direct DME synthesis over physical mixtures of CuO–ZnO–Al2O3 and γ-Al2O3 catalysts was experimentally investigated. Systematic variations in reactor and slit dimensions and configuration were analyzed in terms of thermal behaviour, mass transfer, pressure drop and residence time distribution (RTD). The pressure drop was always small (<0.12 bar) relative to the total pressure (50 bar), and linear dependence with GHSV confirms the predicted laminar flow for Re = 0.1–2. A narrow RTD was estimated by the dispersion analysis. Careful temperature measurements confirmed that the reaction temperature is mainly controlled by the oil heat exchange to give a practically uniform temperature profile for set inlet oil temperatures of 220–320 °C. The micro packed beds were found free of the internal as well as external mass transfer limitations, as showed by no significant change in the CO conversion and DME yield for different catalyst particle sizes, no effect of varying the linear gas velocity, and no effect of manipulating reactant diffusion coefficient. Packed bed microstructured reactors hence provide an isobaric and isothermal environment free from transport limitations for the direct DME synthesis, in the kinetic regime as well as at equilibrium conversion.