Over the last decades, sustainability has ensconced itself in design discourse. We can easily find websites, textbooks and MSc programs in design with a focus on sustainability. There are very few companies, including oil, car and mining concerns, that do not claim to have a strong interest for sustainability. But how do we go beyond the green and blue logos and the fetishistic use of certain materials? Sustainability, when closely examined, reveals itself to be a controversial word for a focus and a set of pratices that are neither without risks nor without costs. Perhaps efficiency, while much more humble, would be a better guiding light for designers.