We previously reported that complete and permanent hydrophilic modification of asymmetric polysulfone (PSf) membranes is achieved via low temperature H2O plasma treatment. Here, we have extended these results to polyethersulfone (PES) and polyethylene (PE) membranes to investigate the role of membrane material (composition) and structure (degree of asymmetry) in the modification. Contact angle (CA) measurements confirm that H2O plasma treatment affords improvement in the wettability of PSf, PES, and PE membranes and XPS results show that H2O plasmas chemically modify all three membrane materials similarly. Differences in the degree and permanence of the hydrophilic modification, however, were observed for PE membranes. Furthermore, environmental SEM images display differences in the depth of hydrophilic modification for PES and PE membranes. Overall, we demonstrate that the extent and permanence of hydrophilic modification of polymeric membranes can be correlated to the mechanisms of interaction between the polymer and reactive species generated in the plasma and the degree of penetration of these species through the porous structure.