Although many new methodological and modelling concepts have been proposed by the scientific community, current industries are still focusing their engineering design process on CAD model since they assume it is the starting point of many analyses with respect to product life cycle (CAM, FEA, LCA…). The paper presents the application of modelling concepts that lead the progressive justification of CAD model with respect to knowledge synthesis by least commitment. Design experts are first formalizing their knowledge that is therefore translated to form features and parameters (topology, position, orientation, dimensions…). The results show that this new design approach and models support design intents and rational, but the generated CAD model is not fully justified. That drives to many conclusions: CAD model is many often non-100% rational by designers’ knowledge, design solution space is therefore larger than the one modelled in CAD software and could be used to foster innovation.