A vacuum are plasma gun configuration was used to deposit metal coatings (Ni and Ti) on polymer (nylon, polytetrafluoroethylene, polyethylene and acrylonitril-butadien-styrene plus polycarbonate) sheet substrates. Using a straight collimated plasma beam, Ni deposition rates of the order of 15 nm s(-1) were achieved, while an additional magnetic quarter-torus macroparticle filter was employed for Ti and Ni deposition at a rate of approximately 4.5 nm s(-1). The deposition process can be divided into three stages. (1) During the initial stage the substrate will have a mass loss dependent on the substrate material and only a small increase in surface conductivity. (2) The second stage is characterized by a constant rate of both mass and surface conductivity increases. (3) For given deposition conditions, substrate surface damage occurs after some critical time. The linear growth of mass and surface conductivity is disrupted and both may decrease depending on the substrate material and the extent of damage. It is hypothesized that the initial stage is dominated by desorption of surface gases and contaminants and possible polymer bond breaking caused by the energetic ion bombardment. Once sufficient surface contaminants are removed and/or sufficient suitable nucleation sites are created by bond breaking, allowing the formation of a continuous metal film, linear growth can commence. Under the high deposition rates (3-15 nm s(-1)) and hence high heat fluxes (about 0.7-3 W cm(-2)) employed in the present experiment and owing to the lack of substrate cooling, the polymer surface eventually reaches its damage threshold limit and substrate damage occurs, resulting in gas devolution and disruption of the conducting path. The practical implications of this study are as follows. (1) The total mass gain cannot be used as a reliable measure of coating thickness on polymer substrates owing to the significant mass loss in the initial stage, which for some substrate materials was larger than the subsequent mass gain. (2) Thermal considerations play a dominant role in limiting the coating thickness in high deposition rate vacuum are metallization of uncooled polymers.