This is a two-part paper where part 1 presents details of a modified wet-filament winding process. Here, the resin bath was replaced with a resin injection system that impregnated the fibres prior to winding them onto a rotating mandrel. The resin and hardener were stored in separate containers and pumped on-demand via a pair of precision gear-pumps to a static mixer. The mixed resin system was then supplied to a custom-designed resin impregnation unit. The theoretical basis for the design of the resin impregnation unit is presented along with simulations of the various parameters that influence the impregnation time and the degree of impregnation. Part 2 of this series papers presents the experimental data on the performance of the resin impregnation unit and a comparison of the physical and mechanical properties of the tubes manufactured using the conventional and modified wet-filament winding techniques.