An elastic, segmented polyurethane fiber obtained by the interaction of a diisocyanate with a glycol. The term “segmented” indicates that it is made from a block copolymer in which reasonably long flexible chains are joined to shorter stiff chains through the urethane linkages. Ref: Mod. Text. Mag. 40, 38 (Dec. 1959); Hicks Jr., Am. Dyest. Rep. 52, no. 1, 33 (1963). Book: Moncrieff, Man-Made Fibres (Heywood, London, 4th ed., 1963) pp 396-403. See: US 2692873 (1954 to du Pont) and US 2751363 (1956 to U.S. Rubber). Compare also Smith, US 3061574; Frazer, Shivers US 3071557 (1962, 1963 to du Pont). Historical review of industrial production with extensive patents list: L. Rose, Rep. Prog. Appl. Chem. 51, 609-612 (1966). Monograph: M. McDonald, Spandex Manufacture (Noyes, Park Ridge, N.J., 1970) 190 pp.