This thesis analyses the use of value models as boundary objects to support decision making during conceptual design of Product-Service Systems. Compared to requirements-based models, value models are claimed to enhance understanding of the design problems and customer needs, as well as to help the design team in creating more value adding solutions. The work of this thesis was to prepare, conduct and analyse a series of design experiments, which are are based on the continuous observations of designers’ verbalized design considerations. Protocol analysis was conducted to investigate how value models perform as boundary objects in design, in comparison with requirements-based models. The time spent on each different activity in the protocol has been used as main proxy in the experiment. Data triangulation was ensured by the use of a questionnaire that was answered by all participants. Both methods revealed that in the preliminary phase, value models are more effective than requirements-based models in conveying intuitive value-related information, assessing intangibles value aspects, and encouraging discussions on value concerns.