Smart materials are materials that change properties according to stimuli, adapting to their environment. This makes them particularly interesting, to increase the performance of a product, and to enable new functionalities and new ways to interact with users. Some smart materials can affect the perception we have of objects. Existing smart materials have an action mostly on the visual and the tactile aspects. The most popular variations are based on colour changing materials, such as thermo/photo-chromic materials or thermo/photo-luminescent ones, and shape changing materials, such as shape memory alloys. These new materials will allow designers to introduce new sensory experiences in their products. For that, they need to know what differentiate these materials from common ones, which kinds of smart material exist, and to have some guidelines about how they can be used. This paper presents a tentative classification of smart material that relates to the way they can be used in product design. This is illustrated through some application examples of colour and shape changing materials.