Gas Shocks Gas-pressurized shock absorbers have been available for over 30 years. Like non-pressurized shocks they use oil as a damping medium. Sometimes you may see the term gas-filled but this is misleading. Gas-filled struts are a form of spring like those used for hoods, hatches and truck lids. In gas pressurized shocks, the oil is pressurized to minimize the negative effects of foaming or cavitation.
Oil has some gas or air bound up in solution.
When the shock piston moves through the oil there is a pressure drop behind the piston and the air comes out of solution and forms foamed oil. For maximum performance and efficiency the shock piston must work in clear oil. However an inexpensive poor quality low-pressure shock is no bargain.