A study examined the effects of loom speed, air jet time, air pressure in the main nozzle twist factor of the filling yarn, spinning method, and filling yarn count on the rate of twist loss of filling yarn during weft insertion on air jet looms. Increasing the loom speed reduced insertion time and decreased twist loss significantly. Shorter duration air jet blasts resulted in higher loss of twist. Higher air pressure in the main nozzle increased the difference between air velocity and yarn velocity and increased the untwisting action of the jet. Filling yarns with higher twist levels required increased insertion times, which increased loss of twist. Due to their higher linear density, coarse yarns required longer insertion times. However, finer yarns exhibited higher twist loss than coarser yarns. Ring spun yarns generally exhibited more twist loss than open end yarns. 22 refs.