High tenacity, high modulus polyamide yarn and process for making same

A yarn comprised of a polyamide which is at least about 85% poly(hexamethylene adipamide) or poly( epsilon -caproamide) is disclosed which has a relative viscosity of greater than about 50, a tenacity of greater than about 11.0 g/d, a dry heat shrinkage at 160 DEG C of not more than about 6.5 percent, a boil-off shrinkage of less than about 7%, a modulus of greater than about 35 g/d, a birefringence of greater than about 0.060, a differential birefringence D: DELTA .90-.00, of greater than 0, and a sonic modulus of greater than about 90 g/d. The process for making the yarn includes drawing of a feed yarn while heating to at least about 185 DEG C in at least a final draw stage to a draw tension of at least 3.8 g/d, subsequently decreasing the tension while heating to at least about 185 DEG C to produce a length decrease of between about 2 and about 13.5, and cooling and packaging the yarn.