People with Duchenne muscular dystrophy (DMD) will suffer from a limited hand function. Therefore, a dynamic hand orthosis could be one of the solutions to improve their hand function and quality of life. However, at this moment, none of the obtainable hand orthoses fits their special needs. The goal of this research is to design a flat dynamic hand orthosis finger for DMD patients with Brooke scale grades 4, 5, or 6 and to test its functioning. The design consists of a silicone outer part, and an inner part from polylactic acid. The presented prototype is small, can generate a flexion movement and has a finger mass of 20 g. Output forces were tested in horizontal and vertical direction and different designs were compared in relation to the bending angle. The reached output forces in horizontal and vertical direction with a certain pressure were 3.4 N (10.5 N target) at 1.75 bar and 0.6 N at 2 bar, respectively. The bending angles were 35◦ for the MCP joint, 78◦ for the PIP joint, and 58◦ for the DIP joint. To conclude, this paper presented a new design of a finger for a hand orthosis. The prototype is flat, can generate flexion movements and has a finger mass of 20 g. Except for the MCP joint, the bending angles meet the requirements. Only the output forces were too low. An outer structure of another material might solve this.