Kevlar sheeting is 20 pounds for a 5m^2 roll, I thought I would have a fairly thin steel sheet with a layer of kevlar underneath that and then a layer of rubber/foam underneath that.
Kevlar didn't seem that expensive, and could make up for the lighter sheet of steel, I mainly chose steel for welding purposes, but I'm looking into ali welding, I don't want to go into acid baths to remove slag just for a lighter armour that might cost more anyway, I could do a steel/ali mix, bolting the ali and welding the steel.

What are the pros and cons of using different materials?
i.e. Steel, ali, poly carb, wood etc.

Thanks as always for your answers so far!