Cloth is a deceptively simple word. We all think we know what it means, since we are constantly in contact with cloth as clothing and in our homes. Because cloth is so much a part of our daily lives we take it for granted—our minds do not question this wonderful substance and the myriad of guises it comes in. A cursory examination of the two magnified cloth samples shown in Figure 1.1 gives a hint of the complex underlying structure of cloth and how much this structure can vary between fabrics. How is cloth formed or made? What gives one kind of cloth a particular set of characteristics not found in another? These questions may not occur to the average person, but when one models and simulates cloth for computer graphics, answers to these questions are of great importance. As one obtains a deeper knowledge of cloth, a whole new world opens up that has many surprises and questions in it.