Resin Infusion (RI) is one of the Liquid Composite Moulding processes, and is increasingly being used to manufacture high performance composite structures. Application of a flexible bag as one part of the mould results in laminate thicknesses varying significantly during filling, and in the period after filling, during which final laminate quality is reached. A 2.5D RI simulation has been developed, and is compared to detailed experiments for three moderately complex preform shapes. Evolution of resin pressure is predicted with good accuracy, and laminate thicknesses changes are moderately underestimated. SimLCM is demonstrated to be superior to a constant thickness Resin Transfer Moulding simulation, and is currently being extended to model the post-filling period.