This paper focuses on activated carbon cloths used for VOC treatment. The studied device is a cylindrical pleated filter that is developed for the implementation of these materials in dynamic systems. 3-D numerical simulations of flows have been performed to determine the flow structure in this kind of geometry. The analysis of the flow structure reveals preferential flow directions in the pleated medium. The local velocity range near the fabric could be 10 times higher than the average velocity calculated for the whole developed surface of the filter, but even the maximal value of the velocity (0.3 m s(-1)) is acceptable for adsorption. Overlap phenomena are revealed and dead zones estimated. The influence of the number of pleats in such a device on the aerodynamic performance is also studied. (C) 2003 Elsevier Ltd. All rights reserved.