The application of numerical simulation to wearable airbags for motorcyclists is relatively recent and only few works about this topic can be found in the literature. This research uses multi-physics simulation to analyse a new wearable airbag geometry, primarily designed to protect the shoulders of motorcycle riders, with the aim of assessing the effect of inflation pressure on the protection performance. The finite element model of the airbag employs a simple linear-isotropic material model, calibrated though the comparison between experimental and numerical outcomes of a drop test, together with the analysis of the airbag inflated geometry. The finite element model of the wearable device is then fitted to a dummy model and a human body model, in order to be used in a parametric analysis. Two set-ups are considered. The first is a thorax impact test, used to assess the effect of inflation pressure on chest protection. A modification to the bag geometry is also proposed and tested on this configuration. The second set-up is a shoulder impact test, used to assess the effect of inflation pressure on shoulder protection. In both tests an optimal inflation pressure can be found, but the maximization of shoulder protection proved more critical and should therefore drive the choice of this parameter.