One of the most actual and consistent driver for industry is sustainability. This topic opens at different problems according to the three sustainability pillars: environment, economic, and social. Regarding the last one, there is a lack for methodologies and tools. Moreover, industries are crossing today a crucial transition in terms of technologies. The so called fourth industrial revolution is ongoing. This is a second challenge for industries that needs to be competitive reducing their time to market integrating new technologies on their production sites. From these perspectives, this work is aimed at highlighting the role of the humans under the Industry 4.0 paradigm. A new transdisciplinary engineering method to favour the sustainable manufacturing is provided. It allows designing a connected environment (IoT framework) aimed at measuring and promoting social sustainability on production sites. The work also remarks the relationship between social sustainability and productivity. Indeed, optimizing the human works permits to improve the quality of the working conditions while improving efficiency of the production system. The case study was performed at an Italian sole producer. The goal of the analysis was to improve and innovate the finishing area of the plant from a social point of view with the perspective of digital manufacturing. An IoT framework has been installed, without affecting the productivity, and the work of 2 operators has been compared in order to identify common problems and define a synergy strategy.