Abstract: A synthetic polymer hollow irregular multifilament yarn useful for producing bulky yarn products comprises a plurality of hollow irregular individual filaments each comprising a hollow filamentary constituent, a non-hollow sinuous filamentary constituent sinuously extending in a wave form along the hollow filamentary constituent, having a smaller average thickness than the hollow filamentary constituent and being connected to one side of the hollow filamentary constituent through a middle filamentary constituent distortedly extending along the hollow filamentary constituent and having a cross-sectional profile in the form of a waist, and is produced by extruding at least one polymer melt through a spinneret having a plurality of spinning orifices each consisting of a first orifice segment adequate for forming a hollow filament, a second orifice segment adequate for forming a non-hollow filament and having a smaller cross-section than that of the first orifice segment and a third orifice segment in the form of