Sunflower is an ideal example of a totally utilisable nonfood industrial crop. The oil is used to produce biodiesel and the oil cake, the extraction byproduct, is a valuable candidate to make 100% natural thermoplastic composites. Made of the remainings of crushed kernel and husks, sunflower oil cake (SFOC) is composed mainly of storage proteins and lignocellulosic fibres, which can be considered, respectively, as matrix and fibre reinforcement. Sunflower proteins, structurally close to soy proteins, are known for their plastic properties. They are discussed in the chapter through their thermal behavior (glass transition, denaturation) and their mechanical characteristics of formed materials by casting, thermomoulding and extrusion. Thermomechanical twin-screw extrusion processing of the raw SFOC is a way to perform, in one-step, the plasticisation of the protein matrix, the defibration of the husk and the compounding of the thermoplastic composite. The conditions of such processing are presented including their influence on the SFOC microstructure, protein denaturation and melt rheology of the composite. The effect of the compounding treatment is then related to the mechanical properties of materials obtained by injection moulding. A specific chemical treatment using a food-reducing agent allows optimum properties to be achieved. A preindustrial study of the process is lastly discussed. Examples of industrial materials are presented, some as agricultural transplanting pots, which take advantage of the specific water resistance of these protein-based composites. This example is then developed in terms of economic feasibility (the scale up of the process) and environmental benefits.