The goal of this project is to create a simple simulation more as like a visual aid to a science fair project. I want to let air flow through a porous material and simulate that so others viewing it can see the air flow and mechanics in the real world. I have created 3 parts: the air, the porous material, and the outer shell
The error I am getting is that if I set the outer shell as a wall it says I need to assign it as a material which I can’t do as CFD only has liquids and gases
Hi @StandardCube, thanks for posting on the forum and welcome to the SimScale Community 
It’s not that CFD only allows for fluid materials, but that for particular simulation types (such as Incompressible), we’re only concerned with the fluid portion of the domain. Conjugate Heat Transfer, on the other hand, would allow for thermal interactions between solids and fluids.
The “porous material” could be modeled as a porous media advanced concept.
Since it seems like you’re not concerned with any sort of thermal interaction between solids and fluids, you could simply delete the solid shell and only keep the flow region + porous media. As I had previously mentioned in another interaction, I’d strongly advise that you run some introductory tutorials before continuing with your own model to understand the basic simulation concepts.
Cheers
Igor