The present invention provides a cost effective customization of user interface devices for use with respiratory ventilation systems, such as face masks that may be used for CPAP therapy. By integrating a user specific customize element (15) into a pre-fabricated user interface device (10), increased comfort for a user during use of the interface device (10) is provided. The customized element (15) is adapted to affect the shape of the user interface device making it compliant with at least one user specific body feature, for example, a facial feature of a particular user. The shape of the customized element may be computed from a user specific data set representing an e.g. three-dimensional shape at least one body feature of a user.