Originally published on 08 November 2023 and transferred from the original BusaBoy blog in 2026.
Aluminium or steel? Divers often ask the question as if one material must be better. In reality, cylinder choice is a balance of buoyancy, capacity, working pressure, physical dimensions, availability, corrosion behaviour and the rest of the diver’s configuration.
Steel cylinders
Steel can provide a lot of gas in a relatively compact package and many steel cylinders remain negatively buoyant throughout the dive. That can reduce the amount of separate ballast a diver needs, which is useful with some backmount and drysuit configurations.
The trade-off is that steel needs protection from corrosion. External coating damage and internal moisture deserve attention, and the exact buoyancy characteristics vary considerably between models.
Aluminium cylinders
Aluminium cylinders are extremely common in recreational and sidemount diving, especially the S80 format. They are corrosion-resistant in a different way from steel, but they are not maintenance-free. Threads, neck condition, impact damage and internal condition still matter.
Many aluminium cylinders become more buoyant as gas is consumed and may become positive near the end of the dive. In sidemount that changing buoyancy becomes part of trim management rather than simply a number in a catalogue.
Working pressure is not decided by the word “steel” or “aluminium”
Both materials exist in different designs and pressure ratings. A diver should read the actual cylinder markings and use the correct valve and filling procedure rather than assume a material automatically means 200, 232 or 300 bar.
Travel and availability can decide the question
The cylinder you own at home is not always the cylinder available at the destination. Aluminium S80s are common in many places and that familiarity is one reason they are popular in sidemount. Elsewhere, steel may be the normal local option.
My own choice depends on the configuration
I use aluminium S80s extensively in sidemount because I like how they behave with my rig and because the format is familiar and widely supported. That does not make steel wrong. With another exposure suit, harness, entry or type of diving, the balance can change.
The better question is not “Which material wins?” It is “What does this cylinder do to my complete weighting, trim, gas plan and logistics?”
