The Ergun equation was used successfully to model the air flow-pressure drop characteristics of beds of granulated ferrous sinter feed (a wet deformable particle system). Experiments were performed in a laboratory permeability pot (447 mm high and 130 mm diameter) using sinter feed blends granulated in a 0.5 m diameter granulation drum. The voidage and granule size distribution for each bed were carefully measured. 115 beds were tested, made up from 10 widely varying blends and covering moisture contents from 3.5 to 8%. The best values of the constants for the viscous and inertial terms in the Ergun equation were found by non-linear regression to be (k(1)/Phi(2)) = 323 and (k(2)/Phi) = 3.78, where Phi is the granule shape factor. Using these values, predicted superficial gas velocities agreed with experimental values within +/-15% for a very wide range of conditions. The original values of k(1) and k(2) given by Ergun (150 and 1.75) underestimated the relative contribution of inertial losses to the overall pressure drop and were not appropriate for this system. Over the range of variables covered, granule size and bed voidage changed significantly with moisture content and blend composition. The Ergun equation correctly predicted the effect of these changes on bed permeability, and hence explained the shape of the permeability-moisture curves for all blends.