Assumptions are presented here as limits within which thinking operates. We ask how such limits emerge when people solve ill-structured questions which are akin to design problems. In a pilot study, 22 university students attempted short and long timed versions of such tasks and were subsequently probed about their initial thoughts. We analysed the responses using reflexive thematic analysis, considering the inability to verbalise how a thought comes to mind, imagery reports, and epistemic justification as behavioural traces of limit formation. Five themes were constructed: “Inside the Invisible Limit”, “From My Memory to Meaning”, “Projection While Solving an Ill-Structured Problem”, “Semantic Attributes of Stimuli vs. the Socially Shared Meaning”, and “My Knowledge is Valid: Epistemic Justification”. We propose a model of assumption-making in which an assumption is an emergent limit shaped by factors informed by these themes. These findings offer early building blocks for a theory of assumption-making.

In this paper, we explore alternative concepts of public “third places” through the lens of speculative design artefacts. “Third places” (i.e. neither home nor work) play a crucial role in building and maintaining social infrastructures and supporting well-being. However, access to these spaces is not equally available to everyone. Older adults with limited mobility, for example, or people experiencing loneliness, may find it difficult to participate in public social life or initiate contact through conventional means. This can lead to social isolation and loneliness. Although virtual or digital third places have emerged in recent years as an alternative, they are often not designed with older users' needs and abilities in mind. This work explores how imaginary, non-physical communication spaces can be created through tangible design objects.

Lightweight design is under the premise of same material and manufacturing technology genuinely essential for sustainability and resource efficiency, yet lightweight products are often perceived as less valuable and less robust. This exploratory study investigates how product weight and shape influence perceived value, robustness, and acceptance. A within-subjects study with 35 participants examined three product types representing different usage contexts: a bottle opener, a camping mug, and a pipe wrench. Visually similar product pairs with systematically varied weight were evaluated, complemented by a second study manipulating both weight and shape. Quantitative ratings were combined with qualitative statements to uncover underlying perceptual mechanisms. Results indicate that heavier products are consistently perceived as more valuable and robust, while lighter variants are associated with lower price expectations. Weight differences based on the Weber–Fechner law were partly insufficient to produce significant effects, suggesting the need for larger absolute differences. A moderate correlation between perceived value and robustness was found, while shape effects were limited primarily to robustness perception.

Automation leads to a rise of assistance systems in vehicles, machines and tools. Existing classifications classify those along processing stages and automation level. However, the purpose and the dimension of the assistance were not used as criteria yet. We propose a classification system for assistance systems by the degree of assistance with automation levels, the dimension of assistance, describing the ratio of user and assisted guidance in 3D space, and the mode of assistance, describing the purpose in terms of comfort, performance, and safety. The classification system is tested for general suitability by applying it to an established industry and one rather new to assistance systems.

Implementing sustainable product development requires assessing sustainability performance throughout the product development process. However, companies face a wide range of assessment approaches and lack guidance on how to select and combine them effectively. Research increasingly calls for coherent methodological support, or a methods ecosystem, to enable consistent adoption. This paper addresses this need by combining empirical insights on capability needs related to product sustainability performance assessment with a synthesis of literature on product development phases, decisions, and tasks. A conceptual model is proposed to show how assessment tasks and capability needs change across development stages and to clarify when effectiveness- and efficiency-oriented approaches are required. The conceptual model is intended to advance research on the creation of coherent methodological support for product sustainability performance assessment by identifying characteristics of supports needed in different stages.

Decision makers in product engineering face a high degree of uncertainty regarding targeted action on diverse and dynamic sustainability demands. This paper reports on the application and evaluation of a Guide developed to support decision makers in addressing this uncertainty and initiating targeted sustainability action. The Guide was applied by facilitators in collaboration with product engineering decision makers at a nano-precision positioning technology company to understand, operationalize, and implement targeted sustainability action. The study revealed that applying the Guide indeed led to context-specific sustainability action at the company and reduced uncertainties for decision makers. It also revealed that decision makers desire pre-fixed sustainability conceptions as a means to perceived uncertainty reduction, although working with pre-fixed conceptions reduces context-specificity of sustainability action and, hence, can lead to inconsistencies in implementation resulting in, e.g., economic risks. The results, therefore, highlight that addressing decision makers uncertainty without pre-fixed conceptions of sustainability is important.

This study applies the Design Research Methodology to explore the concept of sufficiency and identify key characteristics of businesses operationalising sufficiency. The literature review revealed the absence of a universal definition of sufficiency and a noticeable gap between the theoretical understanding and practical application. To address this, the study presents a set of sufficiency-driven business strategies and develops the Sufficiency-Driven Business Model Canvas - a framework that clarifies core elements as well as supports companies in developing sufficiency-driven business models.

Circular economy strategies are widely discussed, but their integration into hierarchical product development often lacks structural guidance. This paper proposes a decomposition-point-based framework that allocates strategies within RFLT-based system refinement. A DP allocation review links strategies to requirements, functions, responsibilities and strategy-specific follow-up indicators, considering obsolescence and trade-offs. A BOM-based coffee machine example illustrates the approach.