chain segment length l of at least 40 nanometers as determined at 23 u00b0 c from the low frequency raman band associated with the longitudinal acoustic mode lam 1 in yet another embodiment the invention is a novel polyethylene multi filament yarn comprising a polyethylene having an intrinsic viscosity in decalin at 135 u00b0 c of from 5 dl g to 35 dl g fewer than two methyl groups per thousand carbon atoms and less than 2 wt of other constituents the multi filament yarn having a tenacity of at least 17 g d as measured by astm d2256 02 wherein filaments of the yarn have a value of the u201c parameter of intrachain cooperativity of the melting process u201d u03bd of at least 535 in a further embodiment the invention is a novel polyethylene multi filament yarn comprising a polyethylene having an intrinsic viscosity in decalin at 135 u00b0 c of from about 5 dl g to 35 dl g fewer than about two methyl groups per thousand carbon atoms and less than about 2 wt of other constituents the multi filament yarn having a tenacity of at least 17 g d as measured by astm d2256 02 wherein the intensity of the 002 x ray reflection of one filament of the yarn measured at room temperature and under no load shows two distinct.