The literature on new product development examines a variety of roles that prototypes can play based on the phase of the design process when they are used, but the characteristics of these prototypes that correspond to the expected outcomes, especially in the early phase of the design process, are understudied. We address this gap by studying the characteristics of the prototypes used in the design process (especially during the early phase) that correspond to their roles. Based on an analysis of six cases of prototypes that are used early on in the design process, we characterize three different archetypes of artefacts: stimulators, demonstrators, and validators, and we emphasize the coherence between the role they play in the design process and the characteristics that enable these roles. Specifying the roles of these artefacts should contribute to addressing the two flaws that are generally encountered during prototyping: overdesigning and overtrusting the prototypes.