The factors which affect the textile quality usually known as resilience are discussed, and a normalized co efficient is derived which quantitatively expresses the degree of resilience of textile fibers. Use of the term "elastic performance," rather than "resilience," is sug gested. The dependence of elastic performance upon the fundamental load-deformation properties of textile ma terials is considered and it is demonstrated that the elastic performance coefficient reflects the effect of immediate-elastic, primary-creep, and secondary-creep deflections. The coefficient is indicated to be applicable to all types of loading: tension, compression, bending, torsion, etc. All that is required for its calculation is a load-deforma tion diagram under uniform, controlled cyclical loading and unloading. Data are presented upon the tensional elastic per formance of two different materials—continuous filament acetate rayon and fully drawn nylon—under various magnitudes of tension loading. Variations in elastic performance with yarn geometry—that is, twist—are given for the acetate rayon yarn. The evaluation of elastic performance under com pression and other types of loading will be presented in a future paper.