A method of predicting deflection of a pellicle which will occur during movement of the pellicle in a lithographic apparatus, the method including receiving parameters regarding properties of the pellicle and receiving parameters regarding the expected movement of the pellicle. The parameters are applied to a model which predicts deflection of the pellicle as a function of those parameters. The model includes a plurality of sub-models which relate to different components of deflection of the pellicle. An output of the model may be used to predict.