The increase in competition amongst companies that produce complex or large product portfolios has created a need to utilise modularity strategies not only to flexibly manage technical complexity in a costeffective manner but also for visual appearance. This research aims to understand how the visual appearance of products is affected by modular product development strategies. Specifically, the aim is to understand how such strategies induce constraints and generate possibilities for management of visual appearance in the design process.

Five studies have been conducted during the course of this licentiate thesis. Two were conducted with professionals and students in design, while the remaining three are theoretical studies based on findings in the literature, theory building, and experimental research. The goal has been to investigate how designers work when they are put to the task of changing and developing the designs of complex products that are part of a portfolio. The challenge has been to study what suitable strategies exist that manage complex products and product brands, then investigate how these influence designers’ practices.

The first study examined how coherence towards a product category influences the design of new products. The outcome of the study was a method to explore visual coherence and diversity in the appearance of a product category.

The remaining four studies investigated how modularity, brand management and the redesign of product portfolios influence a design process. The second study described a design phenomenon known as aesthetic flexibility, which was further explored in studies three and five. The outcome from these studies was a proposal for four aesthetic flexibility strategies.

The fourth study investigated in what way portfolio extension strategies found in brand management and design research are related, and how such strategies influence aesthetic flexibility. The results from study four were illustrated as a model.

The main contribution of this work is the phenomenon of ‘aesthetic flexibility’, which helps understand the factors that influence designers when working with branded modular products. Understanding visual flexibility serves as a starting point in further investigations of how different development strategies affect the possibilities for visual product design.

The findings of this work serve to illustrate and explain a complex and multi-facetted design phenomenon which many designers manage more or less intuitively today, thus advancing academics’, teachers’ and professional designers’ understanding of the field.

Competition among companies that produce complex or large product portfolios has created a need to use modularity strategies not only to flexibly manage technical complexity in a cost-effective manner but also to produce visually appealing products. This research aims to understand how the visual appearance of products is affected by modular product development strategies and creates coherent product brands. Thus, this study examines the intersection of design aesthetics, product portfolio management, product brand management, and design management. Specifically, this study aims to understand how such strategies constrain and generate possibilities when the industrial design process concerns itself with visual appearance. 

The main research approach has been qualitative multi-case methodology (Miles et al, 2014; Eisenhardt, 1989) and design theory building (Chakrabarti and Blessing, 2016) that collects data through interviews, experimentation, and theoretical studies based on findings in the literature. Sixteen face-to-face interviews were conducted with design vice presidents, senior designers, and senior design engineers at five Swedish manufacturers from the automotive, MedTech, consumer goods, commercial vehicles, and materials handling industries. 

This approach has resulted in the description of three theoretical models and a design method, product gist, for investigating prototypicality in a product category. Aesthetic flexibility reflects the requirement that under certain circumstances an industrial designer has to plan for future (as yet unknown) changes in a design. 

Each of the three theoretical models has a different focus: one model describes three ways manufacturing companies organise a strategic in-house design function; one model describes how design decisions are made on a general level through an intuitive and knowledge-based judgment process; and one model describes the strategies a manager needs to consider when developing an existing product portfolio and how the strategies influence industrial design practice. 

Understanding visual flexibility serves as a starting point for further investigations of how development strategies affect visual product design. This understanding provides industrial designers insight into how they can develop product systems that share design components across product lines to promote brand identity. The findings of this work illustrate and explain a complex and multi-facetted design phenomenon that many designers manage more or less intuitively today; therefore, this study advances the understanding of the field for academics, teachers, and professional designers.