This paper outlines the development and verification of a finite element model for the filling pressure distribution in a square planform silo with flexible walls. The flexibility of the walls has a marked effect on the pressures, so this is an example of significant granular solid-structure interaction. The predictions are compared with experimental observations obtained in a previous study. Both the state of stress in the stored solid and the pressures imposed on the silo walls are investigated. The results confirm that the horizontal pressure distribution at any given depth at the end of filling is far from uniform, with larger pressures developing in the corners than against the mid-side of the silo walls. They also indicate that the conceptual model proposed from an interpretation of the test results provides a reasonable description. It is evident that the wall pressures in flexible-walled rectangular silos are strongly affected by the stiffness of the stored solid. The economic potential of these findings for silo design is noted.