Aluminum decking is an aluminum extrusion with a profile similar to the above illustration. It is very lightweight as well as strong. (This illustration is a close but not perfectly accurate representation. It is intended only to explain the concept.) Aluminum will, of course, never absorb moisture, and it will not warp.
You have the option of choosing an extrusion that will link the “planks” together in a way that makes the deck waterproof. This is not the only type of decking that can keep the space under your deck dry, but it is a natural solution.
And if you are extremely healthy and manage to outlive your deck, aluminum is never wasted in the recycling chain.
There are some disadvantages though. For one thing, it is more expensive, costing up to two times what a composite deck would cost. While the companies that make aluminum decking offer it in a range of pleasing colors, they make no attempt to make it look like wood. It will look like aluminum. It should be no surprise then that you are more likely to see aluminum in a commercial than residential setting.