This study investigated the ability of an online pressure differential leak detector to assess the quality of seals in 355 ml fiber-based brick-type composite packages. Results of these tests showed that: (1) the minimum leak size detection was 25 mu m in diameter; (2) the leak tester was capable of detecting longitudinal seals made with sub-optimum sealing conditions; and (3) headspace analysis showed that the leak tester will not produce false positives results if the headspace measurement is less than 3.5 cm. The leak detector did not significantly weaken the seals of good packages. The results of this study can be used to verify the efficiency of similar non-destructive leak testers in a commercial environment and to develop a time saving alternative method for sealing quality analyses of brick-type packages. (C) 2007 Elsevier Ltd. All rights reserved.