The properties of bulk insulation in printed circuit boards (PCBs) have become even more important, especially for those with a multilayered or embedded structure. In particular, the spatial distribution of internal charge carriers, mainly due to ionic impurities, is thought to affect the reliability of bulk insulation. Therefore, the effects of humidity and temperature on space charge distribution profiles in a five-layered composite of aramid paper and epoxy resin are studied in this paper. More charge carriers are induced at higher temperatures with humidity. A relative humidity of 55% is high enough to induce a saturated amount of charge carriers in the present samples at 40°C.