The hysteresis loop that brush seals produce when they are stiffness checked has proved hard to evaluate using simple beam theory. The development of a Finite Element Analysis model of a brush seal pack is tracked through from simple beam element models through to complex multi layer non -linear models. The simple beam element models show a good match to simple beam theory but not such a good match to test data. The more complex models exhibit a good match to the test data but an increased stiffness when compared to simple beam theory. The increased stiffness is due mainly to bristle -bristle interaction. Test data is shown on se al blow down and pressure driven stiffening that will be used to further evaluate the model of the brush seal pack