From the perspective of producing damping materials, there are mainly two types of shock absorbers: hydraulic and pneumatic, as well as a variable damping shock absorber.

Hydraulic
Hydraulic shock absorbers are widely used in automotive suspension systems. The principle is that when the frame and axle reciprocate in relative motion while the piston moves back and forth in the cylinder barrel of the shock absorber, the oil in the shock absorber housing repeatedly flows from the inner cavity through some narrow pores into another inner cavity. At this point, the friction between the liquid and the inner wall and the internal friction of the liquid molecules form a damping force on the vibration.

Inflatable
Inflatable shock absorbers are a new type of shock absorber developed since the 1960s. Its structural feature is that a floating piston is installed at the lower part of the cylinder barrel, and a sealed chamber formed between the floating piston and one end of the cylinder barrel is filled with high-pressure nitrogen gas. A large cross-section O-ring is installed on the floating piston, which completely separates oil and gas. The working piston is equipped with a compression valve and an extension valve that change the cross-sectional area of the channel according to its movement speed. When the wheels jump up and down, the working piston of the shock absorber moves back and forth in the oil, causing an oil pressure difference between the upper and lower chambers of the working piston. The pressure oil then pushes open the compression valve and the extension valve and flows back and forth. Due to the significant damping force generated by the valve on the pressure oil, the vibration is attenuated.