This paper explores the potential of robotic needle felting for customized production of nonwoven textiles and their architectural applications. The possibility to program the robotic movement and locally control fiber density and distribution allows the design of nonwoven, heterogeneous materials with graded properties not by differentiating their chemical composition, but rather controlling their mechanical structure. We propose a parametric design and fabrication workflow relying on a 6-axis robotic arm. We describe design techniques for the generation of felted surfaces with varying material properties and their translation to instructions for robotic felting, as well as the physical fabrication setup. Within our research, the ability to locally differentiate material properties is further explored to create three-dimensional folding behaviors. We study how fiber densities affect their folding ability and geometry, examine qualities of resulting edges, analyze how they affect folding and finally design targeted folded structures by informing the felting pattern. While robotic felting has not yet found significant applications in architecture, the designs and prototypes demonstrate its potential in the architectural context, as it suggests new solutions for recyclable, circular building components or surfaces.