Research and development in additive manufacturing with concrete has become more widespread over the last decade. The processes developed range from concrete extrusion, to digital fabrication of formworks and the unification of formwork and reinforcement. Although they enable the production of increasingly material-efficient structures, the individual processes still face various challenges such as implementation of reinforcement, geometrical limitations, scaling and formation of cold joints, in particular because of the layer-based process. This research proposes an alternative method of producing concrete formworks dubbed ‘Eggshell’. Combined with a novel casting technique, its aim is to overcome these challenges and make material-efficient concrete production possible. As concrete is the most used construction material in the world its influence on the construction industry is unprecedented. Of the construction costs of concrete, formwork typically makes up 30-80% of the costs. This means formwork considerations are often a key driver in determining the design of concrete structures. Materials used to construct the formwork also have a big impact on the total ecological costs of the concrete building components. As the lifespan of all formwork is finite, this adds to the already considerable amount of waste generated by the building industry. Furthermore, traditional formwork made from steel or wood is ineffective in producing the non-standard, (double) curved geometry that characterizes many contemporary architectural designs. Using innovative means of formwork fabrication, these non-standard building components can potentially be produced in a more cost-, time- and material-efficient way. Moreover, Eggshell opens up possibilities for fabricating structurally optimized geometry, enabling a more efficient use of resources. The research builds upon previous work done as a part of an interdisciplinary master thesis in a collaboration between Gramazio Kohler Research, the Institute of Robotics and Intelligent Systems and the Physical Chemistry of Building Materials group (ETH Zurich). In the thesis a process was developed in which a thin-shell formwork is 3D printed while a fast-hydrating concrete is simultaneously fed in. By 3D printing the formwork, complex geometries can be fabricated effectively. The printed formwork can potentially also be recycled and reused, making the process fully circular. Furthermore, reinforcement can be integrated into the structures, allowing for the creation of structural building components.