1. Introduction
Recognized as one of the most polluting industries globally, the footwear sector faces substantial challenges related to sustainability and adaptability. The predominance of traditional manufacturing methods, which make it difficult to disassemble and recycle components, limits the possibility of reusing materials, resulting in a high environmental impact. In 2022, global footwear production reached 23.9 billion pairs, with a focus on the sneaker segment, whose popularity and structural complexity reinforce the urgent need for innovative and sustainable solutions. However, conventional manufacturing methods, which often involve permanent joining techniques, make it difficult to disassemble and recycle components, resulting in an unsustainable life cycle and a substantial increase in waste (APICCAPS, 2023; Reference Cheah, Ciceri, Olivetti, Matsumura, Forterre, Roth and KirchainCheah et al., 2013; Reference Rahimifard, Staikos and CoatesShahin Rahimifard et al., 2007).
In addition to environmental issues, sneakers have become a central symbol of lifestyle culture, adopted by a wide age range. This trend places additional pressure on the industry, requiring change to offer products that combine style, functionality and environmental responsibility. Sustainability and customization flexibility are therefore attributes increasingly valued by consumers, who seek adaptable and environmentally responsible design solutions (Reference Ceschin and GaziulusoyCeschin & Gaziulusoy, 2016; Reference DennyDenny, 2021).
In this context, Design for Disassembly (DfD) is established as a fundamental methodology for designing products that can be easily disassembled, recycled or reused at the end of their life cycle. Effective implementation of DfD requires specific guidelines, ranging from product architecture, component design to the choice of joining methods (Reference Abuzied, Senbel, Awad and AbbasAbuzied et al., 2020; Reference Tyler and HanTyler & Han, 2019). In the footwear sector, DfD has emerged as a promising response to the need for sustainable production practices, although its application is still limited and poorly integrated into the market.
Thus, this project, included in Work Package 6 (WP6) of FAIST – Agile, Intelligent, Sustainable, and Technological Factory, aims to transform the Portuguese footwear industry through the design of sustainable and circular products (CTCP, 2024). The objective is to develop an innovative process for creating sneakers that allows a more efficient and responsible manufacturing approach.
The process begins with scanning the user’s feet using a device designed to accurately collect biometric data. After scanning, the information is processed and adapted to a shoe model previously selected by the consumer, enabling customization that considers their specific needs.
The construction of the shoe will be guided by the principles of Design for Disassembly (DfD) and generative design, with the intention of minimizing the waste of unnecessary materials. After design optimization, the resulting model will be 3D printed, ensuring efficient use of resources. This entire process will be facilitated by an application that will guide the user through each step, providing an integrated and effective experience.
Thus, the FAIST project proposes the development of sneaker models based on the principles of Design for Disassembly (DfD) and additive manufacturing. This approach aims to create a more sustainable and flexible life cycle, where materials can be easily disassembled, recycled and reused. The methodology optimizes the production process and reduces environmental impact, while allowing greater customization, aligning with the demands of the current market (Reference Abuzied, Senbel, Awad and AbbasAbuzied et al., 2020). However, the success of this type of product depends on a clear definition of requirements that address all essential aspects in the creation of footwear. In design, requirements are essential, as they guide the entire product development process. Effective identification and classification of requirements allows the organization and prioritization of fundamental aspects. A clear definition of these requirements ensures that the final design meets users’ needs while minimizing environmental impact, fostering innovative and environmentally responsible solutions in the footwear sector (Reference Ulrich and EppingerKarl T. Ulrich & Steven D. Eppinger, 2015).
This article describes the methodology used to identify, quantify and classify the fundamental requirements in the design of sustainable footwear, proposing a framework that translates the project objectives into specific parameters, ensuring compliance with performance, safety and sustainability criteria.
2. State of the art
In recent years, the footwear sector has explored alternatives to traditional joining methods, such as the use of adhesives, adopting solutions that facilitate the disassembly and recycling of components. Models such as Nike’s ISPA Link Axis and Zvezdochka illustrate this approach by eliminating adhesives or introducing modularity to allow component reuse (Gregory Han, 2015; Industry Intelligence Inc., 2023). Similarly, Camper’s Roku model features a modular design that simplifies part replacement and extends the product’s lifespan (Tom Ravenscroft, 2024). These examples highlight the potential of Design for Disassembly (DfD) to reduce the environmental impact of footwear production.
DfD is a sustainable design methodology aimed at creating products that can be easily disassembled, recycled, or reused throughout their life cycle. Key principles include modularity, efficient material separation, and process optimization (Reference Abuzied, Senbel, Awad and AbbasAbuzied et al., 2020; Reference Tyler and HanTyler & Han, 2019). In footwear, applying these principles not only reduces waste but also increases flexibility and product customization, aligning with the needs of modern consumers.
Design literature further emphasizes that requirement definition and management are essential to translate strategic and sustainability objectives into concrete solutions. Identifying, quantifying, and classifying requirements helps organize and prioritize critical aspects, ensuring that the final design meets performance, safety, and sustainability criteria (Reference Ulrich and EppingerKarl T. Ulrich & Steven D. Eppinger, 2015). 3D printing has emerged as a key technology to implement DfD principles. For instance, Dior has produced fully 3D-printed models that simplify recycling and end-of-life disposal (Joseph Furness, 2023). Zellerfeld applies 3D printing in single-material designs to create customized footwear, eliminating conventional production steps and enabling more efficient manufacturing (Cassell Ferere, 2024). In contrast, brands such as Adidas and Reebok have explored 3D printing specifically for shoe soles to optimize performance and ergonomics, without applying the technology to the entire structure (Gregory Han, 2017; Tomorrow’s World Today, 2020).
In this study, 3D printing was employed for prototyping modular models following DfD principles, allowing the evaluation of disassembly, material efficiency, and design flexibility. This approach demonstrates that the technology not only supports practical innovation but also reinforces theoretical concepts of DfD, adding scientific value to the research.
The diversity of approaches in both industry and academic research reflects a gradual transformation in the sector, which is increasingly balancing sustainability and performance, promoting more adaptable and environmentally responsible products.
3. Methodology applied and obtained results
Product development began with problem identification, carried out through an analysis of specialized literature and market trends. This analysis made it possible to identify emerging needs in the footwear sector, with special emphasis on technological innovations and sustainability-oriented consumption patterns. Understanding these changes was essential to integrate the Design for Disassembly (DfD) concept into product development. After consolidating this information, the model represented in Figure 1 was applied, using the collected inputs — identified problem, analysis of the problem, trends, and innovations — to define the product requirements in a structured and efficient manner. This methodology effectively structured the transition between needs and concrete solutions that guided the footwear design. The structure of the process of transforming needs into requirements, illustrated in the flowchart represented in Figure 1, highlights the different phases from identifying needs to defining technical requirements.
Flowchart for identification and classification of requirements for design and development of footwear models for disassembly
Figure 1 Long description
The flowchart illustrates the process for identification and classification of requirements for design and development of footwear models for disassembly. The process begins with inputs including problem analysis, market trends, technological innovations, and innovation proposal. Step 1 involves analysis of the state of the art, identifying pros and cons of existing products, new trends, and technological innovations. Step 2 interprets data in terms of needs, identifying users' latent needs and analyzing gaps and innovation opportunities. Step 3 organizes and transforms data in terms of needs, creating a table of needs divided by categories and prioritizing needs. Step 4 transforms needs into requirements, resulting in a table with the definition of requirements for different categories. Step 5 identifies influencing factors, correlating them with defined requirements. Step 6 finalizes the classification of requirements based on collected data, leading to the output: a final table with identification and classification of requirements.
The first phase focused on analysing current footwear production processes, highlighting the limitations of traditional lasts and the growing shortage of more sustainable and adaptable solutions, such as Design for Disassembly (DfD) and 3D printing.
Next, a comparative analysis of existing projects on the market was carried out, where the implementation of new technologies and sustainability principles were evaluated, corresponding to stage 1 (Figure 1). This study identified the pros and cons of each approach, highlighting solutions with the greatest potential in terms of disassembly, recycling and customization through 3D printing.
Based on these results, problems were identified and later transformed into specific needs. These phases of the process are represented in the flowchart that can be seen in Figure 2, demonstrating the path from the analysis of the state of the art (stage 1) to the formulation of needs (stage 3).
3.1. Interpretation of data in terms of needs
Based on the previous analysis, the data were interpreted and the observed problems transformed into needs for product development, corresponding to stage 2 of the model in Figure 1. The flowchart in Figure 2 illustrates the steps that led to this interpretation. Both explicit and latent needs were considered, the latter being especially important as they reflect aspects that consumers may not express directly, but which, when considered, enrich the user experience (Reference Ulrich and EppingerKarl T. Ulrich & Steven D. Eppinger, 2015).
Example of the process used, from step 1 to 3
The process began with the analysis of the state of the art (stage 1), in which existing projects on the market that apply the concepts of Design for Disassembly (DfD) and 3D printing in the footwear sector were evaluated. Examples such as Zvezdochka/Nike, KI Ecobe and Futurecraft 3D/Adidas were analyzed in detail, along with other projects mentioned in the introduction, and their advantages and limitations were evaluated (Gregory Han, 2015, 2017; INNUS Korea Co., 2017). Each of these projects highlighted specific advantages, such as modularity, customization through digital technologies and flexibility of the materials used. However, they also presented considerable limitations, such as the tendency to accumulate dirt in connection areas, complex assembly processes and the impossibility of replacing worn components, compromising both the durability and sustainability of the product.
Based on the analysis of these examples, the identified problems were organized and transformed into specific needs. For example, the problem related to the accumulation of dirt in connection areas was translated into the need for “sneakers to be easy to clean and maintain”, while the problem of complexity in the assembly processes gave rise to the need to “promote production practices responsible”. These results were achieved based on the Ulrich and Eppinger methodology, which recommends expressing needs in a positive way and focusing on the final objectives of the product, without specifying the technical means to achieve them (Reference Ulrich and EppingerKarl T. Ulrich & Steven D. Eppinger, 2015).
When developing a product that is not yet established on the market, consideration of latent needs proved to be fundamental. These reflect aspects that consumers may not express directly, but whose inclusion enriches the user experience. Anticipating these needs is an essential factor in understanding and meeting end-user expectations, even before the product is launched. By focusing on these hidden needs, it becomes possible to create a significant competitive advantage, offering solutions that respond to implicit demands that are often underestimated by competitors.
In total, 42 specific needs were identified throughout this process, which were organized and classified into distinct categories, ensuring a clear vision and oriented towards the project’s objectives. This procedure made it possible to eliminate redundancies and consolidate a coherent list of needs. Figure 2 presents a visual example of this path, illustrating how the collected data were transformed into problems (step 2) and then into concrete needs (step 3).
In this way, the results obtained not only identify and structure fundamental needs but also provide a solid basis to guide product development, ensuring that it responds to market demands and consumer expectations.
3.2. Organization and categorization of needs
After identifying the 42 needs, they were organized and categorized into five distinct groups, with the intention of facilitating their analysis and prioritization in product development. The first category, Fit and Comfort, encompasses all needs related to ergonomics and adaptation of the footwear to the user’s foot.
The second and third categories, “durability and maintenance”, and “design and customization”, are interconnected, as they both relate to latent needs. The first deals with the resistance and longevity of the footwear, ensuring that the materials withstand daily wear and tear and allow for the replacement of damaged components. The second emphasizes aesthetic importance and customization options, allowing the user to adapt the shoe to their personal style. The interplay between these categories highlights how considering these needs can not only improve the end-user experience but also increase their satisfaction over time. The same applies to the next category, “sustainability and disassembly,” which addresses the adoption of sustainable production practices, ease of disassembly and disposal of footwear.
The last category, “performance and functionality”, covers the needs associated with the functional characteristics of the footwear. This category requires the product to consider the essential needs of support, protection and performance during physical activities, considering aspects such as water resistance, flexibility and grip.
To prioritize the areas that would have the greatest impact on the user experience and the success of the product in the market, an interest scale was applied, classifying the needs into three levels: high interest, medium interest and low interest. This scale made it possible to organize and prioritize needs, giving greater weight to those that have a direct impact on the user experience, without leaving aside those that, although less of a priority, also contribute to the final quality of the product.
As a result of this stage, a table was created that organizes the needs by categories and classifies them according to their importance, which facilitates a clear visualization of the priorities in the development of footwear, as exemplified in Figure 2.
3.3. Transforming needs into requirements
After identifying the needs, step 4 (Figure 1) consisted of transforming these needs into specific requirements, with the aim of guiding the technical and functional development of the product. This process is essential to ensure that the identified needs are effectively expressed in clear and measurable attributes, which can be integrated into the final product design.
The needs were grouped into five main categories, and from these, requirements were defined that cover functional, technical and aesthetic aspects of the product. These requirements were organized into six categories that reflect the main functions and characteristics to be considered in the development of the shoe. Functional requirements ensure that the shoe offers protection, support and performance, fulfilling essential functions in a practical and comfortable way. Material requirements focus on choosing components that are lightweight, durable and suitable for sustainable manufacturing techniques, such as 3D printing.
Ergonomic requirements address optimal fit and long-lasting comfort by adapting the product to the user’s anatomy. Aesthetic requirements value visual design and customization, allowing adaptations without compromising functionality. Safety requirements constitute an autonomous category, ensuring appropriate conditions of use through the definition of criteria such as slip resistance, stability during gait, and protection against potential impacts, thereby contributing to the prevention of risks associated with the product’s daily use.
Finally, sustainability and maintenance requirements promote a broad and responsible life cycle, with materials that allow disassembly and recycling, aligned with ecological practices.
In total, 35 requirements were defined, organized according to the categories mentioned. Figure 3 presents examples of these requirements, demonstrating how they correspond to the needs identified previously. These criteria ensure that all essential areas of development are addressed, including functionality, comfort, sustainability and safety. Thus, the process of transforming needs into requirements allows the final product to be innovative, safe and sustainable.
Following this reasoning, the next flowchart exemplifies the process applied in steps 4, 5 and 6 of the models illustrated in Figure 1.
Example of the process used, from step 4 to 6
Identification of the influencing factor
After categorizing the needs into specific groups, an in-depth analysis was carried out to identify the influencing factors that directly impact the requirements established for product development, corresponding to stage 5 of the model. These factors, of a technical nature, are associated with the functional and operational properties of the footwear, acting as fundamental criteria to ensure that the product requirements correspond to the real conditions of use, guaranteeing both the technical feasibility and the final quality of the product (Reference Ulrich and EppingerKarl T. Ulrich & Steven D. Eppinger, 2015).
For each category of requirements, which includes functional, material, ergonomic, aesthetic, safety, sustainability and maintenance aspects, specific influencing factors were designated, directing the design development process in a coherent and structured way. After consolidating the requirements, the influencing factors that directly impact their application in the technical development of the product were identified in detail. During this stage, aspects such as the selection of materials (including essential parts such as the sole and upper), the design oriented towards modularity and ergonomics, and the manufacturing processes were analysed, with special emphasis on the integration of technologies such as 3D printing. In addition, variables related to the geometry of the product, the typology of materials and their suitability for conditions of use were evaluated, considering aspects such as durability and ease of maintenance. These factors were essential to assess the technical impact of each decision on meeting requirements and user experience. Figure 3 illustrates the correlation between functional requirements and identified influencing factors, establishing a solid basis for informed decisions and guiding subsequent product development.
Final classification of requirements
The practical application of the requirements identification and classification model culminated in the creation of a final table (step 6 in Figure 1). In this document, the information gathered was organized in a structured manner, undergoing a process of detailed analysis and treatment. In Figure 3, this table is represented as an example, where you can see the arrangement of the requirements, divided by categories and numbered to facilitate consultation. The influencing factors associated with each requirement and the respective needs that gave rise to them were also identified, thus resulting in a clear and accessible summary of the entire development. A comprehensive overview compiling all the identified requirements, including their corresponding categories and related needs, is presented in Figures 4 and 5. These figures provide a detailed and structured representation of the final requirements, facilitating consultation and ensuring that all essential aspects are considered in the product development process.
4. Conclusions
This article presented a systematic model for identifying and classifying requirements in the development of sneakers, based on the principles of Design for Disassembly (DfD). The main objective was to establish a methodology capable of extracting functional and technical requirements that meet the needs of consumers, considering the main trends and innovations currently available in the footwear market. The methodology applied proved to be effective in organizing and interpreting user needs, allowing this information to be translated into specific requirements that directly guide product development. Through an analysis of consumer trends and sustainable manufacturing practices, the model provides a sound and adaptable framework to guide each phase of the design process. This model is not intended to be a closed or rigid solution, but rather a flexible framework that can be adjusted as new information or technologies become available. Its application facilitates a clear visualization of the requirements for the next phases of development, promoting a structured and effective transition.
In addition to the identification and classification of requirements, this study establishes a structured basis for subsequent design and development phases. The defined requirements support the translation of Design for Disassembly (DfD) principles into concrete design decisions, guiding material selection, joining strategies, and manufacturing processes. This approach contributes to the development of more sustainable and adaptable footwear solutions, aligned with circular economy principles. Future work should focus on applying and validating this framework in industrial contexts to assess its impact on sustainability and production efficiency.
Final requirements, part 1
Final requirements, part 2
Acknowledgement
This study was funded by FAIST Project – Sustainable and Technological Smart Agile Factory, financed by funds from the “Next Generation EU” program of the Recovery and Resilience Plan (PRR) Ref. C644917018-00000031.
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