The inflation system usually consists of a pressurized cylinder, a regulating valve, two high pressure hoses and two aspirators. The cylinder's volume can be between , pressurized to about with either gaseous Nitrogen (N2), or a mixture of Carbon Dioxide (CO2) and Nitrogen. Once made of steel, most cylinders now are made of aluminum or alloy cores wrapped with fiberglass, or other lightweight, fuel saving materials. The CO2 is used to slow down the rate at which the valve expends the gases.