1. Introduction
Product design plays a central role in driving sustainable transformation processes across various industries. The increasing complexity of social, ecological, and economic demands creates significant challenges for product development. True sustainability encompasses far more than selecting environmentally friendly materials. It requires rethinking product properties and acquiring interdisciplinary knowledge to effectively address diverse, interconnected sustainability goals (Reference McAloone, Pigosso, Stark, Seliger and BonvoisinMcAloone & Pigosso, 2017; Reference Ramani, Ramanujan, Bernstein, Zhao, Sutherland, Handwerker, Choi, Kim and ThurstonRamani et al., 2010).
Despite the increasing awareness of the need for holistic sustainability strategies and the tightening of regulatory requirements, current research indicates that existing approaches often focus primarily on ecological optimization. Social dimensions of sustainability and the potential of user interaction are often overlooked, in engineering even in contexts where human–technology interaction plays a key role, such as vehicle interiors.
Approaches of Design for Sustainability (DfS) have made significant contributions to the integration of sustainability goals into design processes (Reference Bhamra and HernandezBhamra & Hernandez, 2021). Nevertheless, there remains a need for methodological and procedural frameworks that systematically support the development of holistically sustainable products (Reference DemirciDemirci, 2024). It is evident that innovation and fundamental rethinking are challenging to accomplish within the confines of conventional, discipline-oriented development structures. It is imperative to acknowledge that translating complex sustainability objectives into actionable design insights and concrete creative decisions necessitates novel, particularly transdisciplinary, approaches (Reference Sharunova, Wang, Kowalski and QureshiSharunova et al., 2022).
A particularly high potential for change is evident in the early phases of product development (Reference Rusch, Demke, Willems and MantwillRusch et al., 2024). It is imperative to recognise that the fundamental challenge lies in the systematic integration of sustainability-related knowledge (Reference Blizzard and KlotzBlizzard & Klotz, 2012) and values into the design process itself. Transdisciplinary collaboration is regarded as essential for addressing complex societal challenges, yet its practical implementation in design practice, especially in the context of vehicle interior design, remains largely unexplored (Reference Lang, Wiek, Bergmann, Stauffacher, Martens, Moll, Swilling and ThomasLang et al., 2012). The absence of structured approaches that enable designers and developers purposefully including input from other disciplines during the early stages of product development is a matter of concern, as it hinders sustainable innovation (Reference Gould, Bratt, Lagun Mesquita, Broman, Hu, Matsumoto, Kuo and SmithGould et al., 2019).
Therefore, this paper addresses the following research question:
How can transdisciplinary conversation be integrated as structured reflection phases within design processes in order to systematically embed holistic sustainability goals into creative decision-making?
The objective of this study is to develop a methodological approach that deliberately integrates transdisciplinary conversations into the early phases of product development. The approach conceptualizes dialogue as a central design activity that enables shared reinterpretation of problem definitions, reveals value conflicts, and links creative exploration to holistic sustainability objectives.
The proposed method was developed based on two conceptual case studies. In the first case study, the approach was examined in the context of sustainable user interface (UI) design in the automotive sector (Reference Gritzbach, Holder, Dyka, Fischer and RemlingerGritzbach et al., 2025). In the second case study, it was applied within an academic investigation on sustainable shape design in mobile interiors, including the creation of corresponding design concepts (Reference Dyka, Gritzbach, Holder and RemlingerDyka et al., 2026).
2. Background and related work
Recent design research acknowledges that sustainability requires not only new products but also new ways of thinking, collaborating, and reflecting. Over the past two decades, DfS approaches such as transdisciplinary design, and adapted systemic process models have evolved. This section outlines key perspectives on sustainability and the growing relevance of transdisciplinarity in design research.
2.1. Holistic understanding of sustainability
Sustainability goes beyond ecological aspects and also includes social, economic and institutional dimensions that interact within complex systems (Reference Elkington, Henriques and RichardsonElkington, 2004). A holistic understanding highlights the interdependence of environmental protection, social well-being and economic viability, aiming for balance rather than optimization of a single dimension. This integrated view forms the foundation of sustainable design practice, as it requires designers to consider both material and immaterial impacts of their decisions across the entire lifecycle and within social contexts.
Within this broader understanding, the United Nations Sustainable Development Goals (SDGs) provide a global normative and political framework for sustainable development (United Nations Department of Economic and Social Affairs, 2015). They define 17 overarching goals, each specified through 169 measurable targets and 251 indicators that track progress across environmental, social and economic dimensions (United Nations Statistics Division, 2025). Figure 1 illustrates the 17 SDGs and their hierarchical structure, showing how they are grouped within the environmental, social, economic and institutional dimensions of sustainability.
The 17 Sustainable Development Goals (SDGs) with their hierarchical structure of goals, targets and indicators, and their classification within the environmental, social, economic and institutional dimensions of sustainability. Adapted from Stockholm Resilience Centre (2016)
Figure 1 Long description
A diagram of the 17 Sustainable Development Goals (SDGs) and their hierarchical structure. The diagram is divided into four main categories: Institution, Economy, Society, and Biosphere. Each category contains specific goals, targets, and indicators. The Institution category includes Goal 17. The Economy category includes Goals 8, 9, 10, and 12. The Society category includes Goals 1, 2, 3, 4, 5, 7, 11, and 16. The Biosphere category includes Goals 6, 13, 14, and 15. Each goal is further broken down into targets and indicators, represented by colored squares and circles. An example is provided for Goal 13, Climate Action, which is broken down into targets 1, 2, 3, a, and b.
Although the SDGs were not originally developed for design practice, they offer a shared vocabulary and orientation for aligning design activities with global sustainability objectives. They also help designers reflect on how design decisions may contribute to or conflict with wider systemic goals (Reference ChouChou, 2021).
2.2. Transdisciplinary design
Design challenges related to sustainability are inherently complex and cannot be solved within the boundaries of a single discipline. They involve social, environmental and technological dimensions that require the integration of multiple forms of knowledge. Understanding how different disciplines collaborate has therefore become central to contemporary design research.
The terms multidisciplinarity, interdisciplinarity and transdisciplinarity describe distinct modes of collaboration (Reference Baveye, Palfreyman and OttenBaveye et al., 2014). Figure 2 illustrates these modes of collaboration and the increasing degree of integration and knowledge exchange across disciplinary and societal boundaries.
Multidisciplinary work brings together specialists from different fields who contribute their expertise in parallel, often without deeply integrating perspectives. Interdisciplinary approaches go further by combining disciplinary insights into a shared framework or methodology (Reference Baveye, Palfreyman and OttenBaveye et al., 2014).
Transdisciplinary collaboration, in contrast, transcends disciplinary boundaries. It involves the co-creation of knowledge among academic experts, practitioners and stakeholders outside academia, aiming to address real-world problems through mutual learning and reflection (Reference Sharunova, Wang, Kowalski and QureshiSharunova et al., 2022). Since sustainability strengthens the systemic view of the product (Reference Ries, Wartzack, Zipse, Zipse, Hornegger, Becker, Beckmann, Bengsch, Feige and SchoberRies et al., 2023), this addition of stakeholders is particularly useful. This approach integrates diverse perspectives and fosters shared ownership of both process and outcomes, making it particularly relevant for sustainability-oriented design.
Modes of disciplinary integration from disciplinary to transdisciplinary collaboration. Adapted from Reference Baveye, Palfreyman and OttenBaveye et al. (2014)
Within design research, Co-Design (Participatory) approaches have promoted collaboration and dialogue between designers, users and stakeholders to improve design outcomes and foster empowerment (Reference Zamenopoulos, Alexiou, Facer and DunleavyZamenopoulos & Alexiou, 2018).
Transdisciplinary design extends these participatory traditions by addressing broader societal challenges and integrating different forms of knowledge, academic and non-academic. While Co-Design seeks participation in design, transdisciplinarity aims for co-production of knowledge through design. It thus operates across disciplinary and societal boundaries, linking design practice to research and policy contexts (Reference Lang, Wiek, Bergmann, Stauffacher, Martens, Moll, Swilling and ThomasLang et al., 2012).
Following Reference Lawrence, Williams, Nanz and RennLawrence et al. (2022), this study understands transdisciplinarity as the integration of academic and practice-based knowledge to address socially relevant sustainability challenges through design. This integrative perspective provides the foundation for the method proposed in this paper, which embeds structured transdisciplinary collaboration within established design processes.
2.3. Process models in design practice
Design processes are often described through models that structure phases of exploration, synthesis and evaluation. One of the most established frameworks is the Double Diamond, developed by the UK Design Council (Design Council, 2019). It divides design into four phases: Discover, Define, Develop and Deliver, representing alternating movements of divergence and convergence. Figure 3 illustrates this iterative structure, showing how design expands to explore and narrows to realise solutions.
The Double Diamond process model showing the four design phases and their alternating movements of divergence and convergence, adapted from Design Council (2025)
The first diamond focuses on understanding users and contexts, while the second addresses the development and testing of ideas. The transitions between these phases provide opportunities to pause, reassess and integrate new insights before moving forward.
Recent research has extended the Double Diamond beyond its traditional application as a design management tool toward an inter- and transdisciplinary research framework. Reference Viviani, Gulino, Rinaldi and VangiViviani et al. (2024) propose an Interdisciplinary Double Diamond Model that integrates design and engineering processes through structured collaboration and mixed methods. Their approach expands the second diamond into parallel development paths, enabling simultaneous investigation of multiple product components and creating a shared platform for knowledge exchange across disciplines.
This view positions the Double Diamond not only as a process for guiding design activity but also as a framework for knowledge co-production. It allows for systematic integration of disciplinary perspectives and supports reflection on how design decisions relate to broader social and environmental contexts. In this paper, the Double Diamond serves as the structural basis for embedding transdisciplinary conversations within an engineering design process, linking established design practice with sustainability-oriented decision making.
3. Development of the method
This section outlines the exploratory and qualitative research approach used to develop and apply the proposed method across two design contexts. The further development of the method follows the approach originally conceived by Reference Brown and KātzBrown and Kātz (2009, p. 41-42):
“The evolution from design to design thinking is the story of the evolution from the creation of products to the analysis of the relationship between people and products, and from there to the relationship between people and people.”
3.1. Exploratory research approach
The method for embedding transdisciplinary conversations to create more sustainable product concept ideas was developed and evaluated through two consecutive case studies. The first study focused on sustainable user interface design and served to test the methodological framework (Reference Gritzbach, Holder, Dyka, Fischer and RemlingerGritzbach et al., 2025). The second study, addressing shape design for sustainable vehicle interiors, refined and extended the approach (Reference Dyka, Gritzbach, Holder and RemlingerDyka et al., 2026). Both studies included experts from academic and non-academic fields to ensure a genuinely transdisciplinary perspective.
In the first case study, experts from sustainability research, design practice, psychology, and human–computer interaction participated in structured discussions on how sustainability aspects could be meaningfully incorporated into early ideation and decision-making phases. The study did not produce visual design outcomes but examined how such dialogues influenced designers’ creative reasoning and understanding of sustainability. The results showed that these discussions fostered shared awareness of sustainability trade-offs and helped translate abstract principles into practical considerations for interaction design.
The second case study applied this framework to shape design in the context of sustainable vehicle interiors. It expanded the procedure of the first study by adding a third phase focused on reflecting and commenting on existing design concepts. Experts from design, engineering, mobility sociology, and sustainability research were invited, again combining academic and practice-based expertise. The interviews followed a semi-structured format and lasted 45 to 60 minutes. Prior to each interview, the responsible engineer pre-selected a set of SDG indicators relevant to the specific design context. This pre-selection was tailored to each expert’s field of knowledge to ensure meaningful discussion. During the interviews, experts rated the relevance of these indicators for shape design and reflected on possible implementation ideas and design directions using the think-aloud method. In the final step, experts provided feedback and additional suggestions on design concepts previously developed by the engineer. The structure of these interview phases is illustrated in Figure 4.
Structure of the transdisciplinary interviews, showing the sequence of phases: SDG pre-selection, indicator rating, expert idea generation, and feedback on design concepts
The interviews were analysed qualitatively, and the resulting insights were integrated into the concept development as reflective input. Together, the two studies demonstrate that transdisciplinary dialogue with across both case studies 37 experts from diverse academic and professional backgrounds can serve as a transferable method for embedding sustainability-oriented reasoning into different design tasks.
3.2. Transdisciplinary nature of the interview process
The interviews are described as transdisciplinary because they brought together diverse forms of knowledge, ranging from academic expertise to practice-based insights. The expert group included not only researchers from fields such as sustainability, education and health, but also practitioners such as social workers, self-employed professionals and teachers who contributed perspectives grounded in everyday professional contexts. Although the experts did not interact with one another directly, the sequential structure of the interviews allowed insights from earlier conversations to inform later discussions and enabled an indirect exchange of disciplinary knowledge. In addition, the inclusion of sketches in case study 2 enabled quick and effective discussion and reflection (Reference Bonnici, Akman, Calleja, Camilleri, Fehling, Ferreira, Hermuth, Israel, Landwehr, Liu, Padfield, Sezgin and RosinBonnici et al., 2019). During the interviews, participants developed their own concrete design ideas, which were later integrated into the concept development. This demonstrates that the process went beyond merely gathering external input; it created opportunities for active engagement with sustainability-related design challenges.
Although the method did not involve full co-design workshops, the interviews provided a space for meaningful dialogue in which disciplinary boundaries were crossed and technical ideas emerged collaboratively. In this sense, the approach can be characterized as both transdisciplinary and partially participatory. This applies in particular because some experts were personally affected by the issues addressed, for instance as women, parents or users in health-related contexts. Their dual role as professionals and potential users enriched the discussions and supported design decisions that were closely aligned with real-world needs. In contrast to conventional expert interviews, the conversations were deliberately embedded as reflective loops within the design process. Their purpose went beyond collecting opinions; it involved reframing problem definitions and generating sustainability-oriented design perspectives.
4. Results
This section presents the results of applying the proposed method in two exploratory design studies. The findings illustrate how transdisciplinary conversations shaped the design processes and supported sustainability-oriented reflection and decision-making.
4.1. Results of the two case studies
The two case studies provide complementary insights into how sustainability related design potentials can be identified across different interior contexts. The first case study shows that automotive UIs can address selected SDG targets related to health, safety, mobility access, climate action and gender equality. The analysis indicates that UIs influence sustainability primarily by structuring information, guiding behaviour and shaping users’ perception of safety. The expert interviews support this assessment and point to concrete opportunities such as adaptive modes for different user groups and situational information functions. Overall, the study identifies the UI as a central communication layer that can contribute to several sustainability dimensions.
The second case study demonstrates that the shape of interior elements in mobile environments offers substantial potential to support SDG-related goals. The combined evaluation of SDG indicators and expert interviews highlights that safety, health, inclusion, gender equality and many other sustainability topics can be effectively influenced through shape design. Shape affects spatial perception, privacy, ergonomics and interaction behaviour and thus addresses core human needs. Ecological and economic aspects can also be supported through material efficient geometries and life cycle sensitive form strategies. The developed concepts, including adaptive seating, inclusive armrests, child-oriented haptic areas and improved visibility zones, illustrate the practical relevance of these findings. Figure 5 summarises the resulting design principles and their implementation in the conceptual train interior.
Results of Case Study 2 (Reference Dyka, Gritzbach, Holder and RemlingerDyka et al., 2026), showing sustainability-oriented design principles, their links to relevant SDGs, and their translation into a conceptual train interior
Figure 5 Long description
Panel A: A diagram showing the evolution from design to design thinking, illustrating the shift from product creation to analyzing relationships between people and products, and between people and people. Panel B: A conceptual train interior featuring a child-friendly seat with a table and books, emphasizing inclusive and child-friendly design principles. The image includes icons representing different sustainability-oriented design principles such as being inclusive, child-friendly, feminine, safe and private, adaptive and ergonomic, and efficient across the lifecycle. Additionally, icons link these principles to relevant Sustainable Development Goals (SDGs).
4.2. Embedding transdisciplinary conversation in the design process
The findings from both case studies and the observed positive influence of the semi-structured, transdisciplinary interviews on the engineers’ knowledge and creativity processes form the basis for the method introduced in this section. Building on these insights, this study proposes a methodological extension of the Double Diamond model that embeds transdisciplinary reflection phases into the design process in order to support sustainability oriented design decisions (see Figure 6). The aim is to enable engineers and designers to integrate complex and holistic sustainability considerations through semi- structured dialogue and iterative critical reflection.
The method maintains the four phases of the Double Diamond (Discover, Define, Develop, Deliver) and complements them with three strategically positioned reflection loops. These loops act as structured transdisciplinary moments that guide divergence and convergence more deliberately and ensure that sustainability related insights can be revisited, deepened or challenged at relevant points in the process. Figure 6 illustrates how these transdisciplinary conversations are integrated into the overall design sequence.
4.2.1. The use of context-related SDG indicators
In the Discover phase, engineers begin by broadly examining which sustainability indicators from the SDG framework may be relevant to their design task. This initial reflection involves understanding sustainability in a holistic sense and asking questions such as “What is holistic sustainability in this context?” and “Which aspects of the SDGs can be influenced through design?”. In parallel, and increasingly in subsequent refinement, this general exploration is related to the technical context of the project, such as UI development or shape design in interior design engineering. At this coarse stage, designers first identify boundaries, for example, that interior design concepts cannot influence political systems.
This process transitions into the Define phase, in which a more detailed selection is undertaken. Engineers assess which indicators, understood as concrete representations of different facets of sustainability, can realistically be influenced through their specific design domain and which cannot. It becomes apparent at this stage that addressing social and ecological SDG aspects requires knowledge from multiple disciplines and cannot be answered solely based on an engineering education.
The SDGs are therefore used to ensure that no relevant sustainability dimensions are overlooked.
Moreover working with targets and especially with indicators is often more accessible, since the indicators are formulated in concrete and specific terms. These SDG indicators serve as the foundation and guiding structure for the subsequent transdisciplinary conversations.
4.2.2. Transdisciplinary conversations for knowledge and new ideas
In the Define and Develop phases, the framework introduces structured, semi guided interviews with experts from various disciplines, including fields such as health, education and ecology. Their expertise includes both academic and non-academic knowledge. As described in detail in Section 3.1, the interviews follow a three-part structure that includes an assessment of the relevance of selected SDG indicators in relation to the experts’ fields, the generation of ideas and perspectives on sustainable design opportunities, and the discussion and reflection on early design proposals formulated by the engineers.
The interviews are intentionally used as the starting point for an open conversation. They function as reflection loops that enable engineers to reconsider assumptions, reframe problem definitions and identify potential value conflicts. The conversations broaden the understanding of sustainability and stimulate new design ideas that would not have emerged within a single disciplinary perspective.
4.2.3. Integration of insights into concepts
In the Deliver phase, insights from the expert conversations and the newly gained knowledge inform which ideas are developed further. Design decisions are revisited with regard to their alignment with the selected SDG indicators, and the findings are translated into concrete concepts or prototypes.
Overall, the approach offers a structured way to embed transdisciplinary knowledge into engineering design and supports the integration of sustainability throughout the creative process. In both case studies, the process concludes before final design solutions are produced, creating a clear starting point for incorporating user testing and further evaluation within a standard design process.
Conceptual framework showing how transdisciplinary interviews are embedded as reflection phase within the Double Diamond model
5. Discussion
The results show that transdisciplinary conversations can serve as effective reflective interventions within design processes, helping designers engage more deeply with sustainability related values and goals. Rather than adding a separate analytical layer, the conversations embed reflection into the creative process itself, allowing sustainability to become a guiding principle for design reasoning.
This reflective dimension also contributes to a shift in the designer’s role. Designers move from acting solely as solution creators to participating in dialogue and interpreting complex value systems (Reference DemirciDemirci, 2024). In this sense, the designer becomes a mediator between disciplines rather than the sole originator of ideas.
From a Design for Sustainability perspective, the method supports a more holistic and systemic understanding of design. It links ecological, social and economic aspects by connecting global sustainability objectives, articulated through the SDGs, with context specific design decisions. Through the semi-structured conversations, the method strengthens value clarification, supports systems thinking and adds intentionality to creative choices.
In both case studies, the application of the method was experienced very positively by the engineers involved in the process, who are also the authors of this paper. This informed the development of the presented framework but also introduces a limitation of the research. Engaging with experts from different fields requires openness, active listening and the ability to translate abstract sustainability insights into design decisions. These qualities may be person dependent. To evaluate the method more robustly, additional case studies involving more engineers and experts will be necessary.
Furthermore, the Develop phase was not carried through to completion. Testing the generated ideas to assess feasibility and quality is still outstanding. At this point, user studies could be conducted, for example using the prototype elements from Case Study 2, which can be made partially experienceable through Virtual Reality (VR). Additionally, it must be acknowledged that the current approach remains qualitative in nature and does not yet allow for a quantified assessment of SDG attainment, which represents a further limitation and an avenue for future methodological development.
Despite these constraints, the approach has strong potential for transferability. The integration of reflective dialogue can be adapted to other design contexts such as general product design or service design, particularly since sustainability challenges are inherently complex and interdisciplinary exchange is essential for gaining deeper understanding. Future applications could refine the format of the conversations, which were initiated here as semi-structured interviews moderated by one engineer, to explore their use in collaborative design teams. Overall, the method contributes to embedding sustainability as a reflective practice within design, transforming creativity into a process of continuous questioning, learning and alignment with shared values.
6. Conclusion
This paper introduced a method that embeds structured transdisciplinary conversations as reflective phases within the Double Diamond design process. Based on two exploratory case studies in sustainable user interface design and vehicle interior shape design, the study shows that early dialogue with experts from diverse fields expands designers’ understanding of sustainability and supports more deliberate decision-making. The results indicate that these conversations help reinterpret problem definitions, reveal value tensions and translate SDG indicators into concrete design opportunities. Integrating reflection loops within the Double Diamond allows sustainability considerations to become part of the creative process instead of a separate assessment step.
The main contribution of this work is a methodological framework that operationalises transdisciplinary reflection for sustainability-oriented design. By combining indicator-based preparation with semi-structured expert input, the method offers a transferable procedure for enriching early design phases.
Future research should investigate the use of this method in collaborative team settings and explore how prototype-based user studies can further complement the reflective conversations. Overall, the study highlights the potential of structured dialogue to strengthen systemic awareness and support sustainability-oriented product development.
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