New data are reported on the filtration of binary fibre/titania (rutile) mixtures. The combined use of the Kozeny-Carman equation and Darcy's law is presented and discussed in relation to application in the filtration of binary mixtures. Upon close study, this approach is shown to have its limitations, particularly when significant aggregation takes place between the two solids species. The difficulties in overcoming these limitations from a purely fundamental basis are highlighted, and a semi-empirical model is presented and discussed. This model appears to represent the specific resistance trend with solids composition reasonably well for a wide range of binary mixture filtration data. (C) 2010 Elsevier Ltd. All rights reserved.