There is an artist on Deviant Art, who makes armors for his dolls from real metals.
Picture here.
Another artist (sorry, can't find their account from DA) made barbie sized chainmail.
I, myself have been thinking, if the plastic material used in coffee packages works for material to do plate armor. (The plastic is silver colored from one side, so it might be possible. I'll post pictures, when I get the project done.)
And of course, leather/faux leather works if one wants lighter armor. And I have seen FIMO clay and other polymer clays used for plate armor.