Weight and Dimensions Steel is more durable and stronger than aluminum, which is why tanks manufactured of the latter often have thicker walls to compensate for the lower tensile strength. This, however, makes them heavier than steel tanks. Also, aluminum has a higher rate of heat transfer than steel, so it can melt at lower temperatures. This can be problematic in hot climates like the Caribbean where neither metal is particularly resistant to heat. The weight difference is not very significant. A 20-50 pound tank will make no difference to a diver using either type of regulator. The real advantage of the steel tank is its durability. Aluminum tanks tend to fracture when dropped on hard surfaces such as rocks, while steel ones usually only crack or dent. This is because aluminum has less resistance to stress failure than steel. If you drop your tank you want it to break instead of being completely destroyed so you can get another one! Aluminum also has the disadvantage of being more prone to corrosion. This is because there are more pathways for moisture to enter the tank through tiny holes or imperfections in the surface treatment. Corrosion can cause an aluminum tank to become brittle and dangerous to use. Steel tanks do suffer from corrosion too, but because they are a more effective barrier against water penetration they don't need to be treated with special chemicals to prevent this problem.