In order to cope with the challenges of sustainability, systematic methods have been developed for improving the ratio between usefulness and environmental impact of products. These necessary efforts are however constrained if the surrounding business model patterns are not challenged at the same time. In this article, open source design (OSD) is presented as a potential concept leading towards alternative and eco-efficient production and consumption patterns. Potential advantages of OSD for environmental sustainability are hypothesized and confronted with the analysis of the environmental friendliness of four open source products. Two synergies between sustainable design and OSD are identified (product modularity and design for local manufacturing) as well as corresponding challenges for further research.