The constant pressure filtration characteristics of cellulose fibers, titania (rutile) and mixtures of the two were studied using an automated filtration apparatus. With filtrations at 450 kPa, the average permeability (k(av)) for pure fiber and rutile were approximately 3.2 x 10(-17) and 1.3 x 10(-16) m(2), respectively, with the variation of k(av) with fiber fraction showing a maximum. Similar trends were observed at filtration pressures of 150 and 600 kPa. The porosities (epsilon(av)) of filter cakes formed from pure fiber and rutile suspensions were approximately 0.75 and 0.6, respectively. Interparticle penetration and additive porosity models were applied to the porosity data, and the additive porosity model appeared to better represent the experimental data. Also, the results obtained suggest that abrupt transitions in cake structure occur part way through some filtrations, resulting in anomalous filtration behavior.