pure oxygen. even with a space suit humans can spend too long out on a space walk a normal six to seven hour stint is very tiring. and humans perspire and have to replenish fluids often they put water into their bodies and then expel it as urine that's why astronauts have to wear diapers on spacewalks. humans have one other problem in space they can't tolerate the extreme temperatures we're not directly in the sun the mercury sinks to minus one hundred fifty degrees celsius then they need to be heated but in the sun the temperature reaches over one hundred degrees so they need to be cool spacesuits temperature is controlled by lining it with a system of thin tubes filled with water which can be warmed up or cooled off.