Involving users in the design process: the role of product representations in co-designing CainRebecca 2011 Allowing users to be part of shaping change in new product development can contribute to more successful products. Advances in recent years in digital product representations (such as CAD and rapid prototyping) can potentially offer economic and time-saving benefits to this process. The research in this thesis has generated guidelines to support co-designing activity by exploring the issues of user involvement in the design process, paying particular attention to the use of digital (computer-based) and non-digital product representations to facilitate understanding and communication. The guidelines emerged through empirical research. The first stage of the research explored users' perceptions of physical and emotional product properties through digital and rapid prototyped representations: initial guidelines for Including product representations in co-designing were generated. An Interview study was then conducted to examine the wider issues of user involvement in designing and the use of digital and non-digital product representations from the standpoint of ten practicing - designers. Challenges and barriers to user Involvement were perceived but designers were open-minded to the Idea of digital co-designing. In parallel an audit was undertaken to evaluate product representation technologies for their ability to facilitate co-designing: traditional non-digital methods of sketching and hand-made models were used to develop criteria for this benchmarking. Limitations were found with existing technology and it was apparent that traditional methods (e. g. hand-drawn sketches and models) were better able to facilitate co-designing at this time than digital methods. These findings led to recommendations for future co-designing tools. Co-designing processes were then explored through six practical studies conducted with individuals and small groups of users. Users experimented with designing and making improved handles for a small gardening tool through sketching and day modelling. Design concepts were then taken further into digital media, through 3D scanning, digital CAD images and rapid prototyping and presented back to users for evaluation. Co-designing was also explored through a commercial context with an international packaging manufacturer. Ten users communicated design ideas for improved packaging by triangulation of notes, sketches, discussion and modelling activity. This produced user-led design criteria and commercially valuable concept designs. Important insights were gained into how codesigning may be facilitated within a commercial context and the experiences of the stakeholders. Several pertinent ethical issues such as ownership of ideas, incentives and rewards for user involvement were raised. The thesis concludes with guidelines and recommendations for co-designing, particularly regarding the role of product representations.