In this study, poly(ethylene glycol) diacrylate (PEGDA) was surface grafted, through UV-initiated grafting, on to a microporous polypropylene (PP) membrane in order to develop and control a moisture-sensitive porous structure. Based on the concentration of the PEGDA grafting solution, as well as other variables, the pores of the membrane were filled to varying degrees with cross-linked PEGDA hydrogel, decreasing the pore sizes. This decrease in pore size was highly dependent on the grafting degree, or weight add-on of the grafted polymer. The grafting degree can be controlled by altering various grafting conditions. The surface grafted PEGDA is expected to swell significantly when exposed to moisture, through change in relative humidity or a liquid-borne pathogen, causing the pore sizes to decrease even further. This provides a microporous polypropylene membrane with improved hydrophilicity and moisture-responsive pores. The membranes will have varying levels of breathability based on the amount of moisture exposure. This will allow for a functional membrane that limits the transport of liquid-borne pathogens while providing transport of moisture vapor away from the body.