Design-Durability: Insights from Product Case Analyses

2. 1. Phase 1: Review of Scholarly articles

In this phase, an exploratory systematic search was conducted using two online databases, Google Scholar and Scopus, employing keyword searches with Boolean operators. The search was carefully limited to disciplines relevant to the research objectives — Materials science, business and management, social sciences, economics, arts, multidisciplinary fields, decision sciences, and psychology — while excluding less relevant fields such as medical science, construction, and branches of engineering that are primarily focused on lifecycle analysis, production methods or material durability. However, design-related fields, including design engineering and craft, were included, as they meaningfully contribute to understanding feature continuity and design-durability.

The keyword strategy was designed to capture a broad range of durability-related concepts, including longer-lasting designs, durable design, and design-durability, as well as how specific design features have remained stable across product life cycles. Keywords such as “feature continuity,” “feature longevity,” “feature consistency,” “feature adaptability,” “design continuity,” “design longevity,” “design consistency,” “design adaptability,” “timeless design,” and “product durability” were employed to identify relevant studies (Table 1). These terms cover both emotional and psychological durability, strategic approaches to sustainable design, and philosophies of resilience and timelessness, which are closely associated with design-durability (Jetti & Dhar, 2024).

Table 1

Search string used for the study

While the keyword strategy was comprehensive, it also has its limitations. The emphasis on “feature” and “design” continuity, longevity, adaptability, and acceptance may have led to an emphasis on feature-centric studies, potentially overlooking broader aspects, such as emotional or psychological durability, which are crucial to product design. Furthermore, the absence of terms related to the circular economy, lifecycle assessments, or material durability may have omitted important systemic and technical perspectives. However, keywords like “product durability” ensured coverage of key dimensions, including physical, emotional, psychological, and strategic durability, circular economy, and product attachment.

To ensure methodological rigour, several criteria were applied to the article selection process. Articles were selected based on their novel theoretical contribution and robust research methods, particularly those that have employed empirical evidence, case studies, or innovative approaches to product durability. Only studies explicitly focused on durability — physical, emotional, psychological, or strategic—were included. Articles that lacked a strong connection to product design or durability were excluded from the final selection. Preference was given to studies that provided recent, innovative perspectives, ensuring that the review reflected contemporary trends and challenges in design-durability. Foundational or seminal works were included if they contributed significantly to the field’s theoretical foundations. Studies incorporating engineering, business, psychology, and sustainability perspectives to address product durability in design were prioritised.

This focused approach ensured that the literature reviewed was directly aligned with the research questions. Only English-language articles published between 2000 and 2024 were considered, as most significant research on obsolescence and product durability in design falls within this timeframe (Jetti & Dhar, 2024; Mesa et al., 2022).

This review phase is essential for analysing the literature and identifying significant trends and constructs contributing to the enduring nature of product designs. The findings aim to enrich theoretical frameworks and practical applications in product design.

The inclusion and exclusion criteria followed during the review are shown below:

• a. Inclusion Criteria:
  • • Relevance to design-durability was required, including aspects such as feature longevity, material resilience, emotional durability, or adaptability.
  • • Only peer-reviewed academic articles or conference papers were included to ensure credibility.
  • • Studies had to be in English and have full-text access to be considered.
  • • Articles published between 2000 and 2024 were included to maintain contemporary relevance.
  • • Studies providing significant theoretical or empirical insights on design-durability were selected.
• b. Exclusion Criteria:
  • • Studies from unrelated fields, such as medical science, construction, and non-relevant engineering disciplines, were excluded.
  • • Articles mentioning durability without linking it to product design or obsolescence were excluded.
  • • Non-peer-reviewed publications, such as white papers, blogs, magazine articles, and thesis (Masters and PhD), were excluded.
  • • Articles published before 2000 were excluded unless they were foundational or seminal works in design-durability.

Two trained researchers independently reviewed 5,506 articles, removing duplicates to narrow the pool to 5,320. An initial title-based screening focused on articles strongly associated with product durability and design, reducing the selection to 1,173. These were then subjected to abstract review, and 146 articles were finalized for full-text analysis. Only peer-reviewed articles were considered during this process. Articles published in institutional sources, such as master’s and PhD theses, were excluded. Articles unanimously deemed unsuitable by both reviewers were removed.

Further, 24 articles related to non-tangible studies, such as visual design, have been removed. From the remaining 122 articles, the literature was categorised into two groups: core articles and application-oriented articles. Of these, 97 articles focused on practical applications were excluded, leaving 25 core articles for content analysis. These core articles, which introduced new attributes and theoretical insights into product durability, provide the foundation for exploring the theoretical basis of design-durability. The distribution of the literature is shown in Table 2.

Table 2

Literature distribution across different concepts and strategies

Figure 2

Literature review process

2. 2. Phase 2: Product Analysis and Review

In this phase, various product cases were examined to explore the reasons for the sustained market presence of specific designs. The approach combines two methodologies: comparing products with predecessors with successors and product dissection, as inspired by Aurisicchio et al. (2011) and Laursen & Barros (2022), respectively. Further, the reasons for the feature continuity were enquired using narrative-based enquiry with the participants.

To identify and analyse sustained features and designs, a total of 80 renowned products were initially selected from categories such as décor, transport, home, and kitchen appliances for their iconic or classic designs. The categories of décor, transport, home, and kitchen appliances were chosen because they feature both technologically advanced and classic, iconic products, which are also among the most frequently used in daily life. These products exemplify both functional durability and timeless appeal, making them ideal for studying design-durability. The selection of these products was carried out by the three members of the research team. They ensured that the products would be familiar and easily recognisable to participants. The profiles of the researchers involved are shown in Table 3. Researchers were selected for their expertise in the fields of product design and industrial design. Those who participated in this stage were chosen for their proficiency in design practice and conducting experiments in research.

Table 3

Profiles of Design Researchers

The study filtered the initially selected 80 products to identify those that maintained stability and consistency of features despite technological changes. The objective is to identify models that have sustained and remained in production beyond the typical lifespan of their category. Models that have sustained this way can be considered more desirable than others. Literature defines these average lifespans as 15-20 years for electronics, 7-15 years for kitchen appliances, and 10-20 years for automobiles (Maulia & Halimatussadiah, 2018; Mendjargal et al., 2022; Terzi̇Oğlu, 2013). During product filtration, care was taken to ensure a balanced distribution across hedonic and utilitarian dimensions to prevent bias in participant responses. Hedonic products are highly associated with emotional and attachment aspects, and utilitarian products are heavily associated with functional aspects of the product only (Haug, 2019). This includes five utilitarian (Mosquito rackets, Vacuum cleaners, Wet mops, Lemon squeezers, and Safety razors), five hedonic (Coca-Cola, Chuck Taylor, Cars, Fountain pens, and Table lamps) and five mixed products (Motorbike, Hexa-Dumbbell, and Pencils, Door handle, and Safety Pin) that are the combination of hedonic and utilitarian. Finally, fifteen standout products were identified and placed on a timeline (Figure 3a, 3b, 3c), illustrating their historical context, innovation parallels, and feature evolution.

Figure 3a

Products considered for the study

Figure 3b

Products considered for the study

Figure 3c

Products considered for the study

Product Reviewing

Following the selection of suitable products for the study, participants were tasked with identifying the enduring features, along with the reasons for their continued existence. A standardised protocol was provided to the participants via webmail to ensure consistency, and further clarification was provided through an audio call.

Participant selection

The study required insights from designers, as design-durability deals with enduring features and the design decisions that made them enduring. Twelve industrial designers, each with over five years of experience and a strong background in product design, were selected for the study, with the five-year experience criterion for expertise based on Eteläpelto’s (2000) study. These experts, chosen for their innovative portfolios and diverse real-world product design experiences, are essential for addressing design-durability through their ability to apply practical, innovative solutions across various product categories. The group consisted of eight male and four female industrial design experts from India, each affiliated with fabrication units or design studios specialising in areas such as installations, automotive design, prototype manufacturing, electronics, and medical products. Table 4 details their expertise and backgrounds.

Table 4

Participants and their participatory stage

Procedure and Protocol:

After attaining the final product collection, this segment involved a detailed dissection and analysis of the products across multiple levels to unearth the enduring features of selected products. Since the task is multi-faceted and time-consuming, the study was separated into three levels to accommodate participants’ schedules.

The three levels of the study are as follows:

• a. Level 1: Comparative Analysis
  Participants compared the product’s origin model with its most enduring versions, as illustrated on a timeline in Figures 3a, 3b, and 3c. This step helped identify consistent features and factors that influence core functionalities and usage over time. Insights from this level informed the development of questions for Level 3’s narrative-based inquiry.
• b. Level 2 : Feature and Function Dissection
  The most popular and lasting product models were analysed for their features and functions, as documented in Aurisicchio et al. (2011). For instance, the hexagonal shape of the hexa-dumbbell ensures stability, while the black colour conveys durability and seriousness. Similarly, features and their corresponding functions were analysed. Participants followed a structured protocol (Table 5) to virtually dissect each product, with visual references provided (Figure 3a, 3b, 3c). The protocol outlined specific conditions and examples to guide the analysis of fifteen selected products.
  As industrial and product designers, participants were familiar with iconic products and innovations, which reduced the need for physical samples. Due to geographical limitations across India, physical products could not be provided. The dissection task was completed online within three days, with an example shown in Figure 4. The three-day timeframe provided industrial designers ample time to thoroughly analyse various sensory and functional aspects of fifteen diverse products, ensuring detailed and well-considered evaluations. Due to the virtual nature of the setup, additional time was allotted to account for the absence of physical interaction with the products. When participants had difficulty envisioning certain stages, they were instructed to refer to images and videos of the products for better understanding.

Table 5

Protocol for Level 3

Figure 4

An Example of Product Dissection Performed by a Participant

• c. Level 3: Identifying product features and reasons for continuity
  At this stage, narrative-based inquiry was conducted with the same participants from Level 2, focusing on the longevity of product features and their underlying reasons. In this approach, participants were asked to share their experiences and insights, explaining why specific design elements have endured. Through interviews, participants reflect on their interactions with the products, offering narratives that help identify functional and emotional factors contributing to these features’ longevity. This method provides a deeper understanding of the underlying reasons for feature continuity across product generations. This approach was modelled after the methodology of Haines-Gadd et al. (2018), where participants were engaged in both analytical and reflective processes. Narrative-based inquiry was only conducted on eight participants as data saturation in the interview data was observed, and no new insights on feature continuity emerged. Interviews lasted one to three hours, during which industrial designers were questioned about certain features’ persistence. Images of product models assisted participants in discussing the reasons behind the enduring design elements. A few participants presented their product dissections through sketches. Figure 4 is a compilation of various insights from several designers combined into one visual representation.

Example of a product case: Dyson Vacuum cleaner over time

By comparing models, we can see how Dyson balances continuity and change to stay a market leader in making home appliances.

• a. Iconic features that continued:
  • • Cyclic suction technology was introduced in the 1990s; this core feature prevents suction loss and has been continuously refined.
  • • A transparent dustbin is a consistent feature across models as it allows users to monitor dust levels, enhancing functionality and user trust.
  • • Futuristic aesthetics such as bold, sleek designs with vibrant colours were used across Dyson’s vacuum cleaners.
• b. Iconic features that changed:
  • • Ball technology was introduced in the mid-2000s and helped improve manoeuvrability using a spherical pivot.
  • • Cordless models in the V-series introduced cordless vacuums, shifting towards portability and convenience.

2. 3. Content Analysis

Content analysis was applied to Phases 1 and 2 data, following a procedure adapted from past studies (Kraus & DuBois, 2017; Lettieri et al., 2009; Mayring, 2014; Nag et al., 2022; Xu & Zammit, 2020). This process involved two industrial designer researchers, both experienced in thematic coding, who thoroughly reviewed insights from the literature and product evaluations. The analysis focused on identifying design-durability attributes through a literature review and interviews. Initially, key attributes were derived from the literature, forming the basis for the initial coding scheme. In the second phase, the narrative-based inquiry data attained from product review and analysis was analysed through content analysis, generating new codes that provided further insights into product features and continuity. These new codes were integrated with the literature-based ones to create a comprehensive set of factors.

A hybrid approach was used, combining top-down (theory-driven) and bottom-up (data-driven) methods. The literature informed initial codes, while product review and analysis data revealed emergent themes. Thematic coding was applied to group similar features into broader categories. The example coding scheme is shown in Table 6. Although the literature could have influenced code identification, integrating both data sources provided a thorough exploration of factors driving design-durability.

Table 6

Content Analysis Example

3. 1. Results from the Literature Review (Phase 1):

The concept of design-durability was defined in the literature to explain why certain features continue to exist across products and timelines (Jetti & Dhar, 2024). Though they defined the premise of design-durability with the existing concepts of durable designs and products, their overlap still exists. Identifying these overlaps helped define key attributes of design-durability (Figure 5):

Figure 5

Overlap of Various Similar Concepts with Design-Durability

• • Emotionally durable design focuses on creating products that form deep emotional connections with users. By encouraging attachment and meaningful engagement, the product’s lifespan is prolonged, as users are less likely to dispose of it (Chapman, 2016; Haines-Gadd, 2019). This approach leads products to become iconic within a brand. This approach influences design-durability by ensuring the emotionally significant design elements are featured in new iterations. Both approaches reduce the ecological impact by minimising the frequency of product replacements and contributing to a more sustainable consumption model.
• • Psychologically durable design enhances a product’s perceived value through emotional attachment (Haug, 2019). This approach ensures that users continue to feel satisfied and connected to the product, increasing its functional and emotional lifespan. This aligns with design-durability by preserving iconic and sustaining features across iterations by ensuring a psychological connection that endures.
• • Resilient design aims to create products that are adaptable, repairable, and upgradeable, defying functional and technological obsolescence (Haug, 2018). Emotional durability complements resilient design by promoting attachment. Together, resilient design and emotional durability complement design-durability by preserving adaptable and relevant design elements, allowing products to evolve while maintaining their core design ethos.
• • Timeless design focuses on creating aesthetic and functional elements that stay relevant despite changing trends (Flood Heaton & McDonagh, 2017; Lobos, 2014). Design-durability supports timeless design by ensuring the core features of a product remain aesthetically and functionally meaningful across multiple product lifecycles, reducing the need for frequent replacements.
• • Slow design promotes creating long-lasting, maintainable, and upgradeable products by enhancing emotional connection, reducing the need for replacements, and supporting sustainable consumption (Grosse-Hering et al., 2013). It combats functional and technological obsolescence by prioritising maintainability and upgradeability, ensuring products remain relevant and valuable over time. Design-durability complements slow design by preserving sustainable elements that evolve over time. These elements are carried into future products, countering social obsolescence and promoting durable, long-lasting designs across generations.
• • Physical durability refers to a product’s ability to withstand environmental and physical stresses, ensuring its intended functionality over time (Den Hollander et al., 2017), while design-durability ensures key design features persist as the product endures.
• • Strategic durability aligns product longevity with corporate goals, particularly emphasising sustainability, market presence, and value generation for stakeholders (Razeghian & Weber, 2019). Design-durability complements strategic durability by ensuring that key design features adapt and evolve in line with strategic goals, enhancing the user experience over time while preserving the brand’s core identity.
• • Design DNA refers to the unique aesthetic and conceptual features that define a brand’s identity, ensuring consistency while enabling innovation across product families (Eves & Hewitt, 2009; Rahim et al., 2015; Zhaolin Lu et al., 2009; Zuyao Zhang et al., 2009). Design DNA ensures brand alignment, while design-durability preserves key design elements across product lifecycles, maintaining brand identity and user recognition as products evolve.
• • Design continuity ensures the consistent application of core visual and functional elements across products, maintaining brand identity while enhancing user experience, customer recognition, and loyalty (Althuizen & Chen, 2022; Hsiang et al., 2011; Talke et al., 2017; Yu et al., 2022). In contrast, design-durability ensures that these design features are retained and remain relevant as products are updated or redesigned, supporting both innovation and heritage within product lines.

Upon reviewing the overlap of these various durability concepts, strategic durability emerges as the broadest. It aligns product longevity with corporate sustainability goals and includes slow design, emphasising maintainability and emotional connections. Slow design, as part of strategic durability, promotes sustainability and intersects with resilient design, psychological durability, emotional durability, and physical durability. Resilient design supports design-durability by preserving adaptability, repairability, and relevance, while psychological durability enhances emotional bonds and perceived product value. These bonds connect with emotional durability, resilient design, and slow design to extend product life.

Emotional durability builds strong user attachment, reducing the need for frequent replacements, and links with psychological durability, resilient design, and slow design. Physical durability focuses on withstanding physical wear and intersects with design continuity, timeless design, and slow design. Timeless design ensures long-term relevance and aligns with design-durability, design continuity, and emotional durability. Product DNA defines a brand’s identity and overlaps with slow design, resilient design, psychological durability, and emotional durability to ensure consistency and long-term recognition. Finally, design continuity maintains consistent elements across products, fostering brand loyalty and recognition while supporting timeless design and design-durability.

The 117 factors from 25 core studies on durability, listed in Table 7, were sourced from the literature. However, further verification is needed to identify which attributes best align with design-durability. To address this, we advanced our study by comparing and integrating these factors with those extracted from product reviews, as detailed in the subsequent section. The comprehensive theoretical framework on durability concepts discussed earlier laid the groundwork for assessing the concept of design longevity. This evaluation led to the identification of 35 unique critical attributes. The process of selecting factors from Phase 1 is demonstrated through several examples, as depicted in Table 8.

Table 7

Factors defined from reviewing the literature

Table 8

Content Analysis Example

3. 2. Results from Product reviewing (Phase 2)

During this phase, popular product models or icons were compared to their earlier versions to understand how their purposes have evolved over time and to what extent their design features have been maintained across generations. Similarly, unique and shared features contributing to their enduring presence were identified when competing products were compared. For instance, both Coke and Pepsi bottles feature logos on smooth surfaces, and their bottle openings are perceived as identical. The Pilot Vanishing Point fountain pen has sustained its popularity primarily due to its distinctive retractable nib mechanism.

Numerous products prominently exhibit mid-century modern, modern, art deco, industrial, futuristic, retro, and rustic styles. The study also offers insights into how design attributes—line, shape, form, texture, pattern, colour, space, and size—and design principles, including order, harmony, grouping, proximity, emphasis, balance, proportion, simplicity, symmetry, contrast, and rhythm, contribute to achieving product durability in the market. In phase 2, the narrative-based inquiry and product analysis yielded 253 axial codes.

3. 3. Combined results from Phase 1 and Phase 2

In Phase 3, the combined data from the literature review and product review analysis were examined. This mapping facilitated the identification of 22 factors related to design-durability, as illustrated in Figure 6.

Figure 6

Map of Results Attained in Different Phases of Methodology

Example of content merging from Phases 1 and 2 to form factors based on their affinity and commonality (Clapp et al., 2023) as follows:

• a. Step 1: Combine results from Phase 1
• Phase 1 emphasises timelessness, achieved through traditional, simple, and iconic designs that avoid specific time markers, ensuring long-lasting relevance.
• b. Step 2: Combine results from Phase 2
• Phase 2 focuses on style consistency, using cohesive and symbolic design elements that ensure recognition and adaptability across different contexts.
• c. Step 3: Combine results from Phase 1 and 2
• Style consistency does not completely align with timelessness. However, as product aesthetics evolve while retaining core elements, their combination forms a new concept. This integration allows products to adapt to changing contexts without losing their recognisable identity, resulting in a cohesive and enduring design. A new factor, aesthetic consistency, is created by merging Phase 1’s timelessness with style consistency.

The identified 22 factors are outlined below, further elaborated through product cases from

Phases 1 and 2 to highlight their practical application:

• i. Accessibility: The extent to which a product can be effectively used by individuals with varied abilities is referred to as accessibility. It encompasses the development of designs that are widely usable by accommodating users with varying abilities. The spin mop handle is designed to be lightweight and easy to grip and is an example of accessibility, making it suitable even for individuals with limited strength. The sub-factors that contributed to accessibility are shown in Table 9.

Table 9

Accessibility and their contributing sub-factors

• ii. Aesthetic Continuity: The ability of a product’s aesthetics to remain consistent over time is referred to as aesthetic continuity. Using timeless styles or aesthetics with the ability to reintroduce a product in a different context successfully leads to a product’s aesthetic continuity. Literature states that choosing an appropriate style and aesthetics true to the product’s essence can result in timeless designs (Flood Heaton & McDonagh, 2017). According to Lobos’ research, exceptionally beautiful, nostalgic, or simplistic designs lead to timelessness (Lobos, 2014). Porsche 911 is a notable example of a durable design that has survived the market since 1963 by staying true to its design language. The aesthetics of Chuck-Taylor all-star shoes were popular for basketball sports, and now the same shoes are used for casual wear.

Table 10

Aesthetic continuity and their contributing sub-factors

• iii. Affordance: The cues an object or feature provides about possible usage and activities a user can achieve with them are called “affordances.” These are relational properties between artefacts and users in a given environment. Literature categorised affordance into natural and perceived (Burlamaqui & Dong, 2015). Natural affordance refers to the cues a product’s inherent features provide about its usage to the user. On the other hand, perceived affordance refers to the uses an individual can perceive based on prior experiences and cultural backgrounds. The Zap button in the mosquito bat is an example of natural affordance, as it only allows for pressing downwards and reverts to its original position if not pressed. Many people perceive the fountain pen as a tool for precise and elegant writing; this is an example of perceived affordance.

Table 11

Affordance and their contributing sub-factors

• iv. Engaging Conversations: Conversations are the interactions that happen between the product and the user. Designing feedback mechanisms in a product to make it responsive to the user and environment by improving its perceived dynamic nature can help achieve seamless conversations (Haines-Gadd et al., 2018). Table lamps adjusting their brightness according to the environment’s light can be considered as an example of Conversations (Haines-Gadd, 2019).

Table 12

Engaging conversations and their contributing sub-factors

• v. Evolvability: Evolvability as a design factor is an amalgamation of adaptability and upgradability to change products according to the need (Haines-Gadd et al., 2018). Evolving photo display, a design concept proposed in Haines-Gadd’s doctoral thesis, is an example of evolvability (Haines-Gadd, 2019). This design evolves with time and displays one’s most preferred images.

Table 13

Evolvability and their contributing sub-factors

• vi. Exclusivity: Exclusivity refers to the degree of unique value a product can provide to the user. This characteristic can make an old technology and design appreciable even if new ones exist. Similarly, a product’s exclusivity helps individuals attain status among others (Haug, 2019). Juicy Salif is an example identified among the lemon juicers whose form is differentiated from other juicers, making it exclusive.

Table 14

Exclusivity and their contributing sub-factors

• vii. Harmony: Harmony is the phenomenon in which various elements in a design or product work cohesively and pleasingly together to achieve higher functional efficiency. (Kumar & Garg, 2010). The interaction among design elements, features, products, user’s mental model and environment can lead to harmony. In this context, one example is how the distribution of Dyson vacuum cleaner suction units in combination, helps produce higher efficiency than its individual units. A pair of rubber-coated dumbbells make less noise when used together for certain exercises, making them less embarrassing to use in public. This dumbbell example illustrates how people, products, and the environment all work together harmoniously. Products in an environment that does not have harmony are not used for long. For example, table lamps which are used to create room ambience get replaced if they do not have harmony with other products in the room.

Table 15

Harmony and their contributing sub-factors

• viii. Identity: Identity refers to the characteristics and personality of a product that differentiates it from others. The expression, connectivity and self-discovery a product facilitates can make a user feel the product’s identity (Haines-Gadd et al., 2018). Design that resonates with users can continue to exist for a longer time. Personal assistants are often made to have feminine personalities, as females are generally associated with integrity and pleasantness. Feminine personality in personal assistants is achieved by providing a soft voice and cute forms. Similarly, the concept of DNA, often used in companies to identify certain product features, is constant so that a customer can identify the brand identity and feel the brand value. The best example of this is the kidney front grilles provided in automobiles.

Table 16

Identity and their contributing sub-factors

• ix. Integrity: The quality of design being honest and ethical is considered integrity. It refers to using coherent and consistent systems in a design. It involves upholding a product’s intended purpose, functionality, and aesthetic appeal for its lifespan. Dyson vacuum cleaner, which became famous for its industrial style, not only causes aesthetic appeal but also helps achieve sturdy construction, making them last longer. This is an example of integrity in play.

Table 17

Integrity and their contributing sub-factors

• x. Learnability: Learnability refers to the ease with which an individual can acquire knowledge about using a product or feature efficiently and effectively without making mistakes(Nielson, 1993). Consistent, simplistic, intuitive designs, clear instructions, and familiar entities and metaphors increase product learnability. Making systems easier to learn can thus increase a product’s appeal. Dyson vacuum cleaners with simple, easy-to-use interfaces and buttons are a great example of learnability.

Table 18

Learnability and their contributing sub-factors

• xi. Maintainability: The product’s ability to efficiently achieve resilience through care and repair is called maintainability. Maintenance as an entity includes cleanability and repairability (Joustra et al., 2021). Providing a washable and easily replaceable fabric lampshade in classic ceramic table lamps made them stay popular as a design. This table lamp example illustrates a classic example of maintainability, making the design last longer.

Table 19

Maintainability and their contributing sub-factors

• xii. Maturity: A design or feature is considered mature when it is viewed as fully developed, achieved through iterative optimisation until it meets the highest standards required for a specific product category in a given context. This characteristic offers designers insights into optimised practices that can be adopted to create more effective designs tailored to specific contexts.
  Maturity is achieved in two ways:
  • a. Feature optimisation: Providing the most optimal design feature from the potential solutions for a given context is referred to as feature optimisation. This process enhances product attributes to elevate user experience and value. An example is the addition of a rubber grip on pens to enhance usability.
  • b. Functional optimisation: This approach concentrates on enhancing the functional elements of a product to achieve superior performance within a specific context. For instance, razor blade angles have been progressively optimised to minimise skin damage. Similarly, the ink flow control mechanism in fountain pens is another example where optimisation has been applied to improve functionality.

Table 20

Maturity and their contributing sub-factors

• xiii. Memorability: A user’s ability to recall a product or feature usage is memorability. Consistent, simple, intuitive design features help make designs memorable (Nielson, 1993). Similarly, providing clear instructions and using familiar entities and metaphors can also aid in achieving memorability. The iDrive system in BMW cars is an example of memorability usage in action. The iDrive system is always provided in the middle of the console and helps users easily operate it.

Table 21

Memorability and their contributing sub-factors

• xiv. Narrative: Narrative as an entity informs using shared stories as guidelines in creating features which remind the past product experience and make users experience nostalgia (Haines-Gadd et al., 2018). An example of a narrative is the Bajaj V15 bike, promoted as a piece of history using the material from INS Vikrant, the first aircraft carrier built in India.

Table 22

Narrative and their contributing sub-factors

• xv. Noticeability: The ability of a feature to be seen or noticed is referred to as noticeability. This is accomplished by getting the user’s attention in different ways. Product visibility is the most effective way to get users to notice a feature, among the other senses. Making features unique, recognisable and distinctive makes products visible. The zap button on the mosquito racquet stands out because of its contrasting colour is an example of noticeability. However, noticeability doesn’t always mean making a product or feature stand out. If a product needs to be unnoticeable, it should have design entities that allow it to blend into the environment it is placed in. One example of unobtrusiveness is the form of personal assistants made with fabric-like materials and using neutral colours to blend with their surroundings. This makes people feel comfortable and safe to keep them around.

Table 23

Noticeability and their contributing sub-factors

• xvi. Portability: Portability refers to the characteristics of a product that allow it to be moved from one location to another. Modularity, collapsibility, carriability, and transportability help achieve the portability of a product. A vacuum cleaner’s detachable battery is an example of modularity. This allows users to charge batteries separately and conveniently. Similarly, in the case of a wet mop, storing the wringer by detaching it from the handle allows it to be stored in a compact space. Coke bottles are designed to be durable to withstand the rigours of transportation, demonstrating their transportability. Compact and lightweight safety razors are made to be carried in travel bags with ease, demonstrating carriability.

Table 24

Portability and their contributing sub-factors

• xvii. Production quality: Materials, manufacturing processes, surface treatments, and structural design all play an important role in increasing the lifespan of a product (Joustra et al., 2021). Users always prefer high-quality products when they choose a product. Material plays a prominent role in designing a product as it can also provide a multisensory experience and elicit pleasure. Celebrating imperfections as a concept has happened to be critically defined from the perspective of materials (Haines-Gadd et al., 2018). Also, according to the category, certain materials are used consistently across time in each product. Most double-edged safety razors are made from stainless steel, and cartridge-based safety razors are made from plastic. Similarly, the glass bottle of Coke preserves its taste, making the design continue longer. Anglepoise lamps are an example of production quality, with their structural strength and stable design being vital reasons for ensuring the design’s continuity.

Table 25

Production quality and their contributing sub-factors

• xviii. Proficiency: An individual’s skill level in using a product to achieve a desirable outcome can be referred to as Proficiency (Brownell et al., 2021). Features optimised to proficiency level can increase the efficiency of product use, leading to design continuity. Defining the shape of a pencil is an example of Proficiency: Round pencils are meant for professionals and artists, hexagonals are for moderately skilled users, and triangular for novice users to make writing more comfortable.

Table 26

Proficiency and their contributing sub-factors

• xix. Protection: This attribute refers to the product’s ability to safeguard users or artefacts. Safety, privacy, and security are the three pathways to achieving protection. The curvy razor head, for example, is designed to move smoothly across the face, reducing the number of possible cuts. This design’s safety gives users confidence in using these products. The microphone off button feature provided by Alexa is an example of security and privacy.

Table 27

Protection and their contributing sub-factors

• xx. Redundancy: Providing mechanisms that act as a backup in case of a failure is called redundancy. This can help keep the product running and increase design-durability (Joustra et al., 2021). Bikes are provided with reserve oil storage as they are meant for long drives compared to mopeds, which is an example of redundancy.

Table 28

Redundancy and their contributing sub-factors

• xxi. Standardisation: This process establishes consensus on features and functionalities across industries, companies, and society, covering aspects such as design, materials, performance, and safety requirements. Standardization aids in integrating designs with other products and systems, thereby improving their viability.
  Broadly, standardisation can be classified into four categories:
  • a. Industry standardisation: Industries apply design constraints to enhance product viability. For example, many soft drink companies adopt standardised bottle sizes to reduce manufacturing costs, which allows this feature to remain unchanged. Another instance is the industrial choice to maintain relevance through the inclusion of USB-C ports in most devices today.
  • b. Regional standardisation : This category encompasses socio-cultural norms and values, anthropometric data, and regional working standards. For instance, bike companies in India often release brightly coloured bikes (red, yellow) during peak wedding seasons. Similarly, devices manufactured in the US may not function in India due to differences in electrical frequencies, which can lead to product failure. Consequently, most products are tailored to align with the specific electrical frequencies in India.
  • c. Regulation : Local regulations vary by region. For instance, in India, it is mandatory for bike headlights to illuminate as soon as the vehicle is started. This requirement, enforced by the government, is known as the ‘Daytime Running Light’ feature.
  • d. Design convention : Design choices that are widely recognised and adhered to within a specific domain or industry are called Design conventions. They represent the common methodologies or standards that designers employ when developing a particular design. An example of a design convention is the similarity in interaction layouts across most TV remotes.

Table 29

Standardisation and their contributing sub-factors

• xxii. Versatility: Versatility is defined as a product’s ability to adapt to various situational requirements. Products achieve versatility by being multipurpose or multi-contextual features. Designs created with the ability to do more than one purpose are called Multipurpose designs. Personal assistants are examples of multipurpose devices because they can be used to search information online, as a smart home controller, and to set alarms and reminders. Designs created with the ability to fit varied contexts are called Multi-context designs. For instance, the Zaisu cushioned model became popular among Japanese users for being used in tatami rooms, which was not the context it was meant for.

Table 30

Versatility and their contributing sub-factors

Factors and Design attributes

Further, based on the nature of the identified factors and their relation to the designers’ choices in making a feature enduring. The factors are segregated into six greater attributes of design defined by Ferrerira et al.(2016), as shown in Table 31. The design attributes that were considered for the study are elements of form, organisational principles, communication, function, human factors, and materialisation.

According to Ferrerira et al. (2016):

• a. Form deals with visual and physical characteristics that help build an object.
• b. Organisational principles include the entities that deal with compositional aspects, structure and spatial organisation.
• c. Communication deals with entities that help one understand a feature or a product to convey meaning.
• d. Function deals with the purpose of a feature, its usage, possibilities and limitations.
• e. Human factors inform the subjective aspects of understanding, using and experiencing a product or a feature.
• f. Materialisation informs the physical materialisation aspects such as manufacturing technologies, structures used and built quality.

When the identified factors were mapped, certain factors were observed to be associated with more than one attribute. For instance, Protection as a factor was mapped across both function and human factors. However, protection is regarded as an aspect of function, as it depends on the product’s design rather than the user’s capabilities or interactions. Standardisation and maturity, on the other hand, were commonly observed to be across all factors. These two factors contribute to industrial practices and the market acceptance of a feature over time. Thereby, they are categorised under a new segment named industrial relevance. All the factors identified for design-durability would support designers in identifying features that influence a product design’s survival in the market. For example, aesthetic continuity highlights the most accepted styles of digital devices, which can be used to design a digital audio player. Saregama Carvaan, a digital audio device that succeeded by integrating nostalgic design (AM/FM radio style interface) into modern technology, is one such illustration.

Table 31

Attributes of Design-Durability and Elements of Design