composed mostly of fabric and other soft materials and were custom fitted to each astronaut. The PLSS was back-mounted and completely independent of the spacecraft. An important new feature was the improved cooling system; the astronaut wore a liquid cooling garment (much like long underwear with tubing throughout the fabric) through which water was circulated, absorbing body heat and rejecting it through the primary heat sink, a sublimator in the PLSS. The Apollo EMUs met the requirements for a crewmember operating outside the confines of the Lunar Module spacecraft.

The current Space Shuttle EMU consists of a spacesuit assembly (SSA) and an integrated PLSS. The SSA is made of multiple layers of fabric and other flexible materials attached to a fiberglass unit called the ''hard upper torso." The hard upper torso is the primary structural member of the SSA; the helmet, arms, lower torso assembly, and PLSS are all mounted to it. The PLSS maintains a pressurized 29.6 kPa (4.3 psi), 100 percent oxygen environment for breathing and ventilation. The helmet protects the crewmember against ultraviolet light and provides light attenuation. The EMU also provides some protection from ionizing radiation and micrometeoroids. The PLSS controls the suit pressure, makes up losses from leakage and metabolism, circulates ventilation gas and cooling water to the crewmember, and provides power, communications, and caution and warning systems. The PLSS also removes carbon dioxide, water vapor, and trace contaminants released into the ventilation stream by the crewmember. The spacesuit gloves are the crewmember's interface with virtually all of the equipment and tools he or she uses. The EMU gloves include a pressure bladder, a restraint layer, and a thermal micrometeoroid garment outer layer. The spacesuit and life support system has a mass of approximately 118 kg (260 lb.) when fully charged with consumables for EVA. Tools contribute additional mass. EMU support equipment stays in the Space Shuttle airlock during an EVA; the primary functions of this support equipment are to replenish consumables and to assist the crewmember with donning and doffing the EMU.

For the precursor to the ISS, Space Station Freedom (SSF), a new zero prebreathe suit was initially envisioned.¹ This suit was to be maintainable in orbit by the crew and last for one year of uses, i.e., up to 52 EVAs, without ground maintenance. This new EMU was to reduce the use of consumables, and would have necessitated rechargeable systems for cooling and CO₂ removal on the space station. In 1989, The EVA Commonality Study (Hoffman et al., 1988) concluded