Storm doors can be made of almost any material. Typically, they are made of wood, steel, aluminum, or plastic/vinyl. The pros and cons of each are listed below:
Wood storm doors are probably the cheapest. They are also the oldest. Think of your grandma's old screen door with the huge spring in the middle. It's a classic, old-school look, but most modern houses opt for a metal or plastic composite. However, some of the lower end wood-core doors are durable because they have a plastic or vinyl cover. The downside is if plastic or vinyl is ever scratched to the wood core, as soon as water penetrates the wood expands.
Pros: Cheap, easy to install
Cons: Don’t keep out bugs, don’t seal tight like a storm door, flimsy, easily broken
Aluminum storm doors are one of the most common. You may hear them referred to as "extruded" aluminum frame. That just means "shaped and hollow."
Pros: Heavier, more durable, longer-lasting, and better looking. They look classier and offer much more security.
Cons: More expensive, harder to clean, require more maintenance, and can become hot to touch when exposed to the sun.
If the goal of installing a storm door is to make a thief's life tougher, then you want steel. Unless someone has 30 minutes and a welding torch, they're not getting through these doors. Beware though, the can become a fire hazard because if there's no way in, there's also no way out. Especially if you use a double sided deadbolt and you lose the key.
Pros: High security, need a welding torch to get through the door. Will last a long time.
Cons: Heavy, bulky to install, designed to keep people out but not bugs out, expensive.
Vinyl or Plastic
Pros: Cheaper to purchase, easier to clean, and cheap to replace. With vinyl, the color may be molded throughout. This means that a scratch is less visible because it is not a different color underneath.
Cons: Doors wear out sooner, look “cheaper“, and have trouble standing up to extreme heat and cold.
The bottom line is make sure you buy whatever is in your budget.