Selection of advanced technologies for an evolutionary Space Station Freedom or a planetary (lunar or Martian) extravehicular mobility unit (EMU) will be strongly driven by the system volume and weight, among other factors such as life cycle costs, reliability, safety, etc. A packaging factor will be used to estimate the volume and weight of future EMUs for which the individual component volumes and weights can be determined (by breadboard and preprototype development) but for which the final configurations are not yet known. The purpose of this study is to determine volume and weight packaging factors to be used for sizing trade studies of advanced development Portable Life Support Subsystem (PLSSs). Packaging factors should be based on similar operational systems, e.g., Apollo and Shuttle PLSSs.This paper reports the results of packaging factor studies of both the Apollo EMU PLSS and the National Space Transportation System (NSTS) EMU PLSS. These results can be used as a guide for estimating packaged weights and volumes for advanced PLSS configurations.