The meaning and necessity of stiffness in lining supports are discussed from a theoretical viewpoint. Ten desirable properties of lining fabrics are defined and a survey of synthetic fibers is made. Glass fiber and polyester fabrics are considered to be the most suitable materials. A number of these are tested for stiffness, and the results reported. Significant among these are the existence of high extensions in the bias direction for fiber glass fabrics. Attention is drawn to polyester sailcloth materials, which performed well in the tests. These are specially woven to achieve relatively high stiffness in all fabric directions. -- AATA