This paper proposes a physically-based model for flexible objects such as cloth, rubber, paper, vinyl, and flexible metals. Properties of a flexible object are determined by its basic components such as atoms molecules, and particles, their underlying structure, and their interaction forces. Since even a very thin object such as a cloth has its volume in physical worlds, we decompose a flexible object into and array of unit volumes containing basic components so that they form a crystal structure of basic components and use the elasticity theory to control their interaction forces. The proposed model naturally describes various properties of flexible objects such as stretching, bending, and shearing effects. This model can consistently manipulate both thick and thin objects and also describe the different behavious between a very flexible object and a somewhat rigid one in a uniform way.