The process known as ionized physical vapor deposition, or I-PVD, consists of the physical sputtering of metal atoms into a dense, inert gas plasma; ionization of the sputtered metal atoms, and subsequent deposition of the films from these metal ions. Measurements have shown a decrease in electron temperature coupled with an unexpected decrease in plasma density as a function of increasing metal flux. Recent plasma modeling work has suggested gas rarefaction as the underlying factor in these declines. Measurements of neutral gas density in the plasma region reported here confirm this model and are consistent with earlier studies of sputtered atom induced gas heating and rarefaction.