Scuba cylinders are filled to air pressures ranging from 2000 to 3500 psi (pounds per square inch). To withstand this high pressure, cylinders are carefully engineered from two common materials: steel or aluminum. Both materials have benefits and disadvantages.

Steel is stronger than aluminum, which allows the walls of steel cylinders to be thinner than aluminum tanks. This results in a smaller physical size than aluminum cylinders of the same capacity. The increased strength also makes steel cylinders more resistant to exterior damage. Unfortunately, steel rusts, so special care must be taken to avoid allowing water to enter the cylinder.