Galvanneal steel is a form of hot-dipped galvanized which has an iron-zinc alloy coating on both sides. Galvanneal steel is specially intended for painted application. Compared to regular hot-dipped galvanized, galvanneal has similar corrosion resistance and a harder coating more resistant to scratching. In the fiberglass, galvanneal is used in applications that require superior corrosion resistance and resistance to scratching to a painted product.
Stainless steel is another choice. It has a long lifespan. It is easy to clean and can handle high heat. While stainless steel is more costly than steel and aluminum, it does not rust or corrode easily as ordinary steel. Stainless steel needs no coating. But it does require treatment to remove surface iron that causes rust formation. Fiberglass is the least commonly used material for fans because of its high cost and long fabrication cost. Yet fiberglass continues to occupy an important position in the HVAC industry, where harsh corrosive properties or toxic fumes exist in the airstream. Fiberglass is extremely strong for its weight. It is made up of resin and matting. It requires a gel coat on the exterior because fiberglass resin is not resistant to ultraviolet. Unlike other recyclable materials, fiberglass waste requires proper disposal because the materials are toxic.
As you have seen, there are many different choices as to fan materials. Selecting the right material is based on how the fan is used. Engineers should take into account function, application, strength and durability.