In order to provide optimal air conditions in workplaces the requirements for mechanical ventilation systems are continuously improved. The most popular material used for air ducts is sheet steel. Due to its high costs and susceptibility to corrosion processes, other materials, e.g. PVC (polyvinylchloride) or other plastics should be used as duct materials more widely. Another advantage of plastic air ducts is simple installation, as no additional supporting constructions are required. Flow characteristics for plastic foil air ducts have not been established yet. Therefore, the velocity profile is investigated. The results of the research are compared with the mathematical model of the flow in smooth pipes. (C) 2010 Elsevier B.V. All rights reserved.