In this paper, we present an experimental work using a MOCAP system and an iterative minimization technique to compute damping parameters and to measure their contribution for the simulation of cloth in free fall movement. Energy damping is an important phenomenon to consider for the 3D simulation of warp and weft materials, since it has a great influence on the animation realism. This phenomenon can be generated either by friction between moving cloth and air, or by friction between the warp and the weft threads of the fabric. The contribution of this paper is to determine viscous parameters of cloth using precise trajectory data of a real cloth.