filament 14 is twisted relatively loosely around the elastic performance filament 12 such relative loose twisting of the inelastic control filament 14 about the elastic performance filament 12 thus allows the elastic filament 12 to be extensible under tension until a point is reached whereby the inelastic control filament 14 reaches its extension limit i e a point whereby the relative looseness of the inelastic filament has been removed along with any extensibility permitted by filament texturing crimping that may be present such that any further tensioning would result in permanent deformation or breakage such a tensioned state is depicted schematically in accompanying fig3 it will be understood that since the fibrous sheath 10 2 is comprised of an incoherent mass of entangled randomly oriented spun staple fibers it will permit the extension of the elastic performance filament 12 to occur up to the limit of the inelastic control filament 14 without physical separation furthermore the fibrous sheath itself serves to limit the extensibility of the elastic performance filament 12 albeit to a much lesser extent as compared to the inelastic control filament 14 thus throughout repeated tensioning and relaxation cycles the fibrous sheath 10 2 will continue to visibly hide the filamentary core 10.