The appearance of fabric motion is suggested to affect the human perception of bending stiffness. This study presents a novel spatial augmented reality, or projection mapping, approach that can visually manipulate the perceived bending stiffness of a fabric. Particularly, we proposed a flow enhancement method that can change the apparent fabric motion by using a simple optical flow analysis technique rather than complex physical simulations for interactive applications. Through a psychophysical experiment, we investigated the relationship between the magnification factor of our flow enhancement and the perceived bending stiffness of a fabric. Furthermore, we constructed a prototype application system that allows users to control the stiffness of a fabric without changing the actual physical fabric. By evaluating the prototype, we confirmed that the proposed technique can manipulate the perceived stiffness of various materials (i.e., cotton, polyester, and mixed cotton and linen) at an average accuracy of 90.3 percent.