www.ijdesign.org 41 International Journal of Design Vol.1 No.3 2007 Introduction Products do not only differentiate themselves from other products in functionality, but also in the way that they please users (Jordan, 2000). Users nowadays expect a product to function properly (Roozenburg & Eekels, 1995), to be easy to use, and to touch them emotionally in some way (Desmet, 2002). The moment that products satisfy the consumer on issues like utility, safety, and comfort the emphasis of the consumer will shift towards appearance, emotional attributes, and symbols (Crilly, Moultrie, & Clarkson, 2004). Manufacturers that develop products with these expectations have grown significantly, especially in the consumers market. They have started to realize that they need ways to get into the hearts and minds of their customers to stay in business (Sanders, 2001). Materials selection plays an essential role in the product design process (Doordan, 2003). Product materials determine the range of function, durability, certain costs, user feedback, and user experience. When users interact with products, their senses are in contact with the materials of those products. Users see the colours of materials, feel the texture and weight, and hear the sounds that the materials make when the object is moved. These sensory perceptions contribute to product usability and use experiences (Hekkert, 2006). Product designers use materials to create these sensory perceptions (Ashby & Johnson, 2002, 2003). In addition, product designers select materials for products to elicit the right associations. For example, the metals that are used in a Rolex watch project social status (Jordan, 2000). Hodgson and Harper (2004) stated that materials considerations are pervasive in design as the substance through which product designers��� intentions are embodied. Likewise, Gant (2005) emphasized that the strategic use of materials is one of the most influential ways through which product designers engender deeper, more emotive connections between their products and their users. The materials that a product is made of thus influence how users interact with the product. The different aspects of materials can be for the most part categorized in two groups, namely the technical aspects and the user-interaction aspects. The technical aspects of materials define how the product will be manufactured and how it will function. The user-interaction aspects are those that influence the usability and personality of a product. For example, shininess can influence Received April 23, 2007 Accepted October 17, 2007 Published December 1, 2007 Copyright: �� 2007 van Kesteren, Stappers and de Bruijn. Copyright for this article is retained by the authors, with first publication rights granted to the International Journal of Design. All journal content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 2.5 License. By virtue of their appearance in this open access journal, articles are free to use, with proper attribution, in educational and other non-commercial settings. *Corresponding Author: IlsevanKesteren@gmail.com Materials in Products Selection: Tools for Including User-Interaction in Materials Selection I. E. H. van Kesteren *, P. J. Stappers, and J. C. M. de Bruijn Faculty of Industrial Design Engineering, Delft University of Technology, Delft, The Netherlands Products do not only discriminate from other products in functionality, but also in the way they please users. The sensorial properties of materials influence whether a product provides adequate feedback or gives a pleasant emotional experience. Designing a specific user- interaction involves selecting appropriate materials that create that interaction. However, defining which material properties contribute to the desired interaction is difficult as these are often subjective. Clients are not always able to clearly specify what desired user-interaction they want to create with the product. As a result, product designers often start a search based on unclear criteria. The recently developed Materials in Products Selection (MiPS) tools help product designers together with clients in defining the sensorial properties of materials required to create a desired user-interaction with the product. The tools define the user-interaction via several means, namely pictures of product examples and their materials, actual materials samples, and the sensorial aspects of materials during several phases of the user-product interaction. This paper presents an evaluation of the tools with professionals and students. The results show that these tools lead to high consensus between product designers and clients during discussions and a better definition of the required materials properties. Keywords - User-product Interaction, Client-Product Designer Relation, Materials Selection Tools, Evaluation of Tools. Relevance to Design Practice ��� The materials selection tools offer a practical instrument for the discussions product designers have with their clients about the desired user-interaction aspects of a product and the materials from which it is made. Citation: van Kesteren, I. E. H., Stappers, P. J., & de Bruijn, J. C. M. (2007). Materials in product selection: Tools for including user-interaction aspects in materials selection. International Journal of Design, 1(3), 41-55. orIgInal artIClE

www.ijdesign.org 42 International Journal of Design Vol.1 No.3 2007 Materials in Products Selection: Tools for Including User-Interaction in Materials Selection how well users can read from a display (use aspects) and colours are a very strong aspect to create a personality that influences user experience. For high quality products, product designers should select materials that are optimal or compromise in both aspects. A problem that product designers encounter in materials selection is that their clients are often unable to clearly specify what user-interaction aspects of materials they desire in a new product (van Kesteren, Stappers, & de Bruijn, 2006). Consequently, product designers start a materials search based on criteria that can be interpreted in different ways. Product designers use their experiences to select candidate materials, which they then discuss with the clients. They point out that during these discussions, it is clear that the clients desire aesthetics and perceptions other than initially stated. It is undesirable for the product designers to be on the wrong track too long or for them to have to start from the beginning with a new materials search. This leads to unnecessary delays in the materials selection process. Our aim is to find ways to minimize these unnecessary delays. We developed the Materials in Products Selection (MiPS) tools, which are new tools for incorporating user-interaction aspects into the materials selection process (van Kesteren, Stappers, & de Bruijn, 2007). The tools��� main purpose is to increase understanding and form consensus between clients and product designers about the desired user-interaction aspects of the materials used in a new product. The tools can be used in design brief meetings in which clients explain the objectives and constraints for a new product. The expected benefits of the tools are summarized in Table 1. Table 1. Summary of the expected benefits of the tools Assist clients in clearly specifying requirements that relate to user- interaction Form consensus between the client and product designer about user-interaction aspects in early stages of materials selection so less changes are required later in the project User-interaction criteria are formulated as sensorial material properties. MiPS aims at defining a material profile for a new product in terms of sensorial properties (Table 2 and 3). These properties can be translated later into technical properties and are expected to be concrete enough so that both the client and designer have the same expectations. Descriptions of perception and use are still multi-interpretable and therefore less useful for this purpose. Technical properties can come forward in discussions about user-interaction aspects, but it is not necessary. Preferably the tools do not direct to material names yet. Although defining materials reduces the number of possible material candidates, it can also lead to problems e.g., when the materials cannot fulfil project objectives on other aspects aside from user-interaction. Furthermore, new materials are easily excluded when materials are defined at the beginning of a project. In the next section, we present the three MiPS tools. Thereafter, we study the tools in a fictive design brief meeting, as shown in the ���usability study,��� ���results,��� and ���discussion��� sections. Furthermore, based on the results of the study, we present a revised version of the tools at the end of the paper. Materials in Products Selection: three tools MiPS consists of three different tools for design brief meetings between product designers and clients. The tools define user- interaction through several means- pictures of product examples and their materials (picture tool), actual materials samples (sample tool), and the sensorial aspects of materials during several phases of the user-product interaction (question tool). Picture tool Example products are an important frame of reference in the early phases of product development (Pasman & Stappers, 2001). When a product designer wants to create a certain personality, he can use existing products and the materials from which these products are made as examples. Together with a client he can select those aspects of the example products of which they think create the desired personality. The background idea of the tool is to offer product designers a set of product images for defining the sensorial properties that create a specific product personality. We expect that clients in particular can better point out what they want from example products than in terms of material characteristics. Govers (2004) developed a product personality scale in which product personality refers to the character of a product. This scale consists of 20 personality terms that are visualized with pictures. These pictures show situations and objects, not necessarily products. For the picture tool, a similar set of images was made, but of existing products. To create uniformity in product examples, a product category was chosen, namely consumer electronics, in which most products can be characterized. Numerous pictures of products were selected from various internet stores and were categorized under 20 personality terms. During the categorization, we found the term ���pretty��� to be more subjective than the other terms. It more closely relates to the product itself rather than the materials. The same holds for the term ���idiosyncratic.��� We omitted both terms in the final set. The terms ���serious��� and ���boring��� appeared to have the same products associated with them. The materials aspects of these products were similar. We decided to replace these two terms with the term ���business like.��� Also the terms ���provocative��� and ���lively��� were combined into the term ���lively.��� Ilse van Kesteren has dedicated her PhD project on materials selection in product design. Her work concentrates on the activities of product designers that lead to specific materials for products that require both high technical and user-interaction standards. The project resulted in tools that improve the communication concerning sensorial properties of materials. Pieter Jan Stappers is a full professor in Design Techniques. His interests focus on developing techniques and tools that support designers (and other creative people) in the early phases of idea and concept development. Key elements of this work, carried out in ID-Studiolab, are contextual studies, visualisation techniques using traditional and new media, and development of interactive prototypes. Sjef de Bruijn is a part-time professor in Designing and Manufacturing of Plastic Products, as well as the director of product development at Flexcell, a Swiss company that manufactures ultra thin, highly flexible, and light weight photovoltaic (PV) cells, and modules. Moreover, he works as a consultant at Fresh Innovation, an office for (the management of) fast innovation in product design.

www.ijdesign.org 43 International Journal of Design Vol.1 No.3 2007 I. E. H. van Kesteren, P. J. Stappers, and J. C. M. de Bruijn After selecting appropriate product examples, the picture cards were composed. The picture tool consists of a set of 16 cards with each representing a different personality. On the front of the card are product examples that help the visualization of personality. The back of the card helps to translate the product characteristics into sensorial properties (Figure 1). It shows details of the materials and some keywords. These cards can be used in two steps. While defining a design brief, clients can show which personality cards are representative of their desired product personality (using the front). Next, product designers can discuss the sensorial properties related to the selected personalities with the client using the back. An example of a question that the product designer may ask the client is ���These products are semi- transparent, is that also what you had in mind?��� The product designer can then begin a materials search based on these material properties. The picture cards will vary somewhat depending on culture, trends, and time. The product examples used in the cards for this study are products that are available in the Netherlands and placed on the cards by Dutch design students. The connection between the personality term and the product examples are made within their context and might be different in another context. These connections, however, do not determine the outcome of the discussions, but rather inspire discussions. In other words, if a client wants to create a ���lively��� product, it may not necessarily be similar to the products presented on the ���lively��� card. It is the combination of cards and the aspects that come up in the discussion that are directing the materials choices for the product. Hence, disagreement between the tool user and the creator can be inspiring. Furthermore, the discussions should not focus on the products themselves but on the material properties that these products represent. However, we do acknowledge that in due time, example products might need to be replaced or that in other cultures other example products will be more suitable. Sample tool Material samples are widely used in materials selection (van Kesteren, 2008). They are used as a communication tool for comparing and testing candidate materials. Material samples from suppliers show, for example, different colours or different transparencies of their material portfolios. The idea is to use samples in the defining phase of materials selection, thus to formulate a material profile. The existing sample sets from suppliers are too detailed to use for this purpose: they only vary on some material aspects. A set of samples that represents a wide range of sensorial properties can support the defining phase. These samples help the discussions on which materials best fit the desired user-interaction aspects. In particular, tactile aspects are most suitable for discussions with physical samples. The number of samples is limited to the practical issues of storage, bringing it to client meetings, and using it in discussions. Table 2. Categories of properties that can be used to describe a material profile Property Description Examples Perceptual (P) Most subjective includes perceptions, emotions and associations of materials, brands, or products Outdoor look, modern, personal, recognizable, fit the target group, natural Use (U) All words related to usage Usability, withstand harsh environment, hygienic Sensorial (S) Less subjective all aspects of materials that can be sensed Texture, warmth, colour, softness, smoothness, stiffness (Table 3) Technical (T) Least subjective material and manufacturing properties Scratch resistance, durability, price, suitable for mass production Materials (M) Concrete: material names Plastics, wood, metals table 3. list of sensorial properties Reflection Pressure Sound reflective ��� not reflective denting ��� not denting muffled ��� ringing glossy ��� matte soft ��� hard low ��� high pitch transparent ��� translucent ��� opaque fast ��� slow dampening soft ��� loud not bright ��� bright massive ��� porous rough ��� smooth Smell and taste regular ��� irregular texture Manipulation natural odour ��� no odour ��� fragrant stiff ��� flexible fragrance Colour ductile ��� tough flavour hue of colour brittle ��� tough one colour ��� many colours light ��� heavy Temperature colourless ���colourful warm ��� cold dark ��� light Friction durable ��� faded colour sticky ��� not sticky Light radiation pattern dry ��� wet ��� oily low ��� high light emission rough ��� smooth