Most products are developed by New Product Development (NPD) teams, composed of specialists that need to collaborate closely. One of those specialists is a user-centered designer, focusing on the usability and experience of use of products. In this qualitative empirical study the contribution of designers to NPD teams is explored, filling a gap in literature. It is found that the user centered framing of designers, their imaginative capabilities and their well-developed expressive skills, have a particular contribution to NPD teams. It enables to span complex boundaries inside NPD teams, e.g. between hard- and software engineers or between marketing and R&D. Designers themselves are not nominated boundary spanners, rather the boundary spanning capabilities is a by-product of their design practice. We named this 'mirroring', which is conceptualized as the dynamical and ongoing redrafting of representations of the intended product, enabling team members to align and coordinate activities cross-disciplinary. The implications concern NPD (management) and design (management), as it sheds a new light on what designers (need to) do and the contribution to NPD teams.