The jamming mechanism is an important method to tune the stiffness of soft-bodied machines to enable them to adapt to their surroundings. However, it is difficult for the present jamming structures to integrate them into complicated structures such as twist, cylinder, and spiral. This paper introduces a novel jamming mechanism termed a filament jamming technique, which varies stiffness using jamming of a cluster of tiny and compliant filaments. The jamming structure demonstrated a variety of characteristics such as softness, shape compatibility, lightweight, and high stiffness, which these feats can meet to a variety of application scenarios that the traditional jamming one cannot afford. The mechanical behavior of the jamming structure was studied with an experimental test, in which the experimental results illustrated that its structural and material factors affect stiffness variation and dynamic performance. To demonstrate the advantage of the jamming technique, we constructed a soft gripper and a torsional actuator to demonstrate how the mechanics of filament jamming can enhance the performance of real-world robotics systems. Therefore, the filament jamming mechanism provides a variety of machines and structures with additional properties to increase forces transmitted to the environment and to tune response and damping. This study aims to foster a new generation of mechanically versatile machines and structures with both softness and stiffness.