The paper presents a test method for evaluating air leakage in rodless cylinders with longitudinal slot and sealing band. To this aim a specific test rig was developed in order to carry out leakage tests under different operating conditions. Specifically, the performance of the sealing system consisting of the band, seal, and barrel is analyzed, identifying the critical conditions and factors that influence operation. Particular importance was assigned to selecting band and seal cross-sections in order to minimize leakage and thus limit energy consumption. A final rodless configuration with considerably reduced leakage was proposed.