We know that the atmosphere at the Earth's surface produces a pressure equal to the weight of a large automobile on each square meter. We do not notice this since it is equal both inside and outside our bodies. But if the air inside a metal pot is, for instance, forced out by boiling water inside it, the pot collapses under this pressure.
Similarly, an unprotected astronaut in a space flight would not only die by swelling up, but his blood would also start to boil. The temperature at which a liquid boils depends on the atmospheric pressure. At a height of 9 km, water boils at 74°C; and above 19 kms, blood boils below body temperature. At zero pressure, the astronaut's blood would instantly turn to a deadly loam.
Therefore, keeping these aspects in view, a space suit is specially designed so as to protect an astronaut from the dangers of space during space flights. Space dangers include extreme temperature, hazardous radiations, fast moving particles, vacuum etc..
A space suit clothing is made or several layers each of which has a specific purpose. One of the inner layers controls the temperature. With the help of this Manned Maneuvering Unit (MMU), an astronaut can leave the space craft and fly independently. It has the provision for oxygen gas. Each suit has got a primary life support system. It holds enough water and oxygen to enable the astronaut to carry out space walks for several hours. The space suit has the liquid cooling and ventilation system. In tact each suit is made from a number of different pieces. Each piece is made by selecting the sizes. Individual astronaut is given a suit from these so as to fit him.
One very surprising thing about MMU is its weight On earth it weighs about 158 kgs but when used in space it makes the astronaut very mobile. This is because or the weightlessness conditions in the space. A space suit therefore is a life-saving device for an astronaut.