probably different than the fiber used in the production doll. The ends on the production doll look a little frizzy, so the production doll probably has a cheaper hair fiber like acetate which can't hold a set as well as a more expensive fiber. My guess is the prototype doll hair is a more expensive fiber. The hair color on your doll looks very good and she is awfully cute even if she is not what you expected. You can probably get all of your money back in selling her.
It is probably hard to mass produce an interesting doll with a lot of articulation at a $20 price point. I am sure Mattel has cut corners. I don't know how these dolls will age, but they are fun enough for the moment.