A simple model of a rotating duct cleaning brush was presented using large deformation elastic theory. The results obtained with the model were compared with the results obtained by a laboratory test. In particular, the effect of air drag on the behaviour of the brush was considered. The results show that with normal brush properties, air drag increases the torque needed and reduces somewhat the contact force between a bristle tip and the duct surface. However, air drag has only a slight effect on the deflections of the bristles at the practical rotating speeds of the brush (300-1000 rpm) in a round duct. The modelled and experimental results for the torque caused by air drag were in good agreement in the case where the brush rotated without contact and when a reduced air speed coefficient of 0.5 was used in the simulation. The developed model can be used as a first step in the systematic design of rotating brushes. However, further research is needed to determine the relationship between bristle tip contact and cleaning efficiency. (C) 2004 Elsevier B.V. All rights reserved.