Eco-efficiency in Product-Service Systems (PSS) is one of today's challenges for achieving sustainability and reducing the environmental burden of our production and consumption patterns. However, there are few eco-design methods and tools for the development of eco-efficient PSS and some issues are still not solved for systematic design of environmentally friendly PSS. This paper aims to show that the 'design buckle' object - previously developed in the PSS literature - is a concept which can support the system design by enabling the generation and comparison of alternative solutions. An environmental assessment can be performed on the buckles and facilitate the design process for providing eco-efficient PSS.