The function of negative pressure protective clothing is to establish negative pressure around the lower body of human body, and apply longitudinal load to its supporting muscle tissue to prevent it from being hindered by long-term weightlessness. The negative pressure protective clothing used on the Soyuz is "Phoenix-headed Mackey" type, which is made in the form of airtight pants, and the waist part of the pants is rigid. The bellows shell of the trouser leg is made of air-tight fabric. Several metal rings in the shell are used to prevent the trouser legs from contracting when negative pressure is established. Bellows-like folds help the shell to contract in the axial direction, and at the same time exert a load on the muscle tissue, the support of the human body. The trouser legs are connected with shoes made of aluminum alloy.

The waist is equipped with an airtight "waist", woven belt and instruments. The waist is made of coated tape and tied to the astronauts with tape. The instrument has vacuum regulator (throttle mechanism), vacuum (safety) valve and vacuum indicator.

The vacuum degree (negative pressure) in clothes is provided by a portable device equipped with a vacuum pump. The vacuum pump is driven by a motor. The air in the cabin enters the clothes through the vacuum regulator, then flows into the pump body from the clothes, and then queues up in the environment, thus establishing the vacuum degree in the clothes and realizing ventilation.

Tightening the cover of throttle mechanism can reduce the gas consumption of clothes and increase the vacuum degree in clothes.

The above-mentioned clothing with lower body negative pressure has many advantages in structure, which is better than the fixed (volume) bag with the same function. This unique clothing can prolong the decompression time according to the requirements of preventing cardiovascular changes. Astronauts put on this costume and then connect the onboard system of the spacecraft with cables. The cable length is arbitrary. Therefore, astronauts almost retain the freedom to move in the orbital station and can take various postures to exercise their professional duties. The clothing structure ensures that it can be used for a long time, is convenient to use and has good internal ventilation.

This protective suit is designed with a vacuum of 8.6 kPa (65 mm Hg) and a valve to prevent the vacuum from suddenly rising beyond this limit.

After negative pressure is established in clothes, as long as the corrugated part is folded tightly or the rubber rope is tightened, a force can be generated and acted on the body. Under the action of the above force, the waist and one leg of the body are compressed; If a shoulder strap is added, its function can be extended to the whole spine. Pant legs have certain rigidity, which hinders leg movement, that is to say, this kind of clothing has the inherent performance of loading protective clothing.

The establishment of negative pressure in clothes can produce a feeling of putting your head up. It is not only the redistribution of pressure that contributes to this feeling, but also the pressure on the soles of the feet. In the simulated gravity state of the aircraft, the gravity protective clothing always feels the feet below after work.

The pressure acting on the body is directly proportional to the vacuum degree in the clothes. When the vacuum degree is about 6.6 kPa (50 mm Hg), the pressure acting on the body is equal to 450 ~ 550 N. At this time, the leg movement is difficult and the kinetic energy is significantly increased. But at rest, when the vacuum degree is lower than 40 kPa, the kinetic energy consumption remains unchanged.