Steel vs Aluminum Cylinders in Sidemount
There Is No “Best” Cylinder
The Biggest Difference Is Buoyancy
Aluminum Cylinders
Steel Cylinders
Bigger Isn’t Always Better
Think About Your Team
Consider the Type of Diving You Do
Your Configuration Must Match Your Cylinders
There Is No Universal Answer
Final Thoughts
There Is No “Best” Cylinder
One of the most common questions asked by divers transitioning into sidemount is:
Should I dive steel or aluminum cylinders?
Unfortunately, the answers often sound overly simplistic.
- “Steel is better.”
- “Aluminum is more versatile.”
- “Everyone in cave diving uses steel.”
None of those responses are accurate, and the reality is more complicated. Neither steel nor aluminum cylinders are inherently better. Each has advantages and disadvantages, and the best choice depends on where you dive, how you dive, and what you expect your equipment to do throughout the dive. Understanding those differences is far more valuable than simply following what everyone else is using.
The Biggest Difference Is Buoyancy
When divers compare cylinders, they often focus on capacity or weight. Underwater, the more important consideration is:
How the cylinder’s buoyancy changes during the dive.
As gas is consumed, every cylinder becomes lighter. The amount of that change depends on the cylinder’s design and material.
Many aluminum cylinders become positively buoyant near the end of the dive, especially toward the cylinder bottoms. That buoyancy change affects cylinder trim and positioning.
Steel cylinders generally remain negatively buoyant throughout the dive, resulting in less change in how they handle underwater. Trim and positioning of some steel cylinders are still affected as the dive progresses.
Neither characteristic is inherently good or bad. They simply require different approaches to rigging and configuration.
Aluminum Cylinders
Aluminum cylinders are extremely popular for recreational sidemount diving and are more commonly seen in cave diving in Mexico.
Advantages
- Readily available at most dive destinations
- Easier to rent while traveling
- Lighter to carry on land
- Commonly used in open-water sidemount courses
- Often less expensive to acquire
Many divers who travel frequently appreciate being able to use rental cylinders instead of transporting their own.
Disadvantages
As gas is consumed, aluminum cylinders become increasingly buoyant.
This means:
- cylinder position changes during the dive
- lower attachment points may require adjustment
- proper bungee tension becomes more important
- bungee positioning can affect cylinder trim
- trim can change as the dive progresses
A well-configured sidemount system accommodates these changes, but they cannot be ignored.
Steel Cylinders
Steel cylinders are common among cave and technical divers.
Advantages
- Smaller buoyancy swing throughout the dive
- More consistent cylinder position
- Most have excellent trim characteristics
- Often preferred for overhead environments outside of Mexico
- Reduced (not eliminated) need to compensate for cylinder buoyancy changes
Many divers appreciate the predictable handling steel cylinders provide from the beginning of the dive to the end.
Disadvantages
Steel cylinders also have trade-offs.
They are generally:
- heavier to transport
- more difficult to travel with
- not commonly available as rentals
- sometimes oversized for recreational diving
- the vast variety of steel cylinders makes it so there isn’t a single solution for trim and positioning issues
For divers who fly frequently, these factors may outweigh their underwater advantages.
Bigger Isn’t Always Better
One misconception is that larger cylinders are automatically the better choice. More gas sounds appealing, but cylinder selection isn’t simply about capacity.
Larger cylinders may:
- alter trim
- increase drag
- affect weighting
- require teammates to volume match
- be unnecessary for the dives being conducted
The “best” cylinder is the one that matches the dive, not the one that carries the most gas.
Think About Your Team
Cylinder selection should never happen in isolation. Consider what type and size cylinders your regular dive partners use.
Matching cylinder volume often simplifies:
- gas planning
- turn pressures
- reserve calculations
- team procedures
Choosing significantly larger cylinders than everyone else may sound attractive, but it can complicate team gas management. Equipment decisions should support the team, not just the individual diver.
Just because you have the largest cylinders on the team doesn’t mean you can use all of the gas in them. Adjustments must be made so that you and your teammates are properly gas matched.
Consider the Type of Diving You Do
Ask yourself:
Where do I dive most often?
If your dives are primarily:
- tropical reefs
- recreational open water
- travel destinations
Aluminum cylinders may make the most sense.
If your dives are primarily:
- caves
- technical dives
- local freshwater systems
Steel cylinders may offer advantages in consistency and handling.
The answer depends on your diving, not someone else’s.
Your Configuration Must Match Your Cylinders
One mistake many divers make is changing cylinder types without adjusting their sidemount configuration.
Different cylinders often require changes to:
Simply clipping in a different set of cylinders and expecting identical performance rarely works. Treat every cylinder type as part of a complete system.
There Is No Universal Answer
It’s tempting to ask:
“What cylinders should I buy?”
A better question is:
“What cylinders best support the diving I actually do?”
The answer depends on:
- environment
- travel requirements
- team configuration
- dive objectives
- personal preference
Good sidemount divers choose equipment based on function, not popularity.
Final Thoughts
Steel and aluminum cylinders are simply different tools. Each excels in different situations. The goal isn’t to find the universally “best” cylinder. The goal is to choose the cylinder that best supports your diving while allowing your sidemount configuration to remain balanced, streamlined, and predictable throughout the dive.
Ultimately, the diver, not the cylinder, is what determines the success of the dive.
For a complete overview of how these elements work together, see The Complete Guide to Sidemount Diving Configuration.
Readers of this article can receive $10 off the book Sidemount Diving or $5 off the book Recreational Sidemount Diving when purchasing directly from the website.
Use code TANK10 for the Sidemount Diving Guide and TANK5 for the Recreational Sidemount Diving Guide during checkout.
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