I've never seen discussion on a proper material to make a poppet. It's usually whatever you have on hand at the time. You could make it out of food stuffs, like dough. You could mold one out of wax, sew one with fabric and fluff, paper, all sorts of things. It's pretty fair game.
Agreed with ChennyVoo, I have also never seen it state the correct material to use, you can use anything from straw, to clay, to childrens felt if you want (this is what I have used in the past), it all depends on what you feel comfortable with using, and what you have around.
In hoodoo there are many ways to make poppets I have many wax poppets but they can also be made from American Mandrake this is mainly for love some people make theirs of cloth and stuff herbs and petition inside some make them out of sticks. I personally have made poppets or doll babies out of Licorice root for controling someone. If you dont know what you are doing I suggest research this subject more.
In hoodoo they are almost always referred to as doll-babies, and they can be made from a variety of different materials; most often people just used what they had at hand. So for instance you can use a barbie or action man or something similar, and personalize it with personal concerns.
Or if you make a cloth one, you would generally stuff it with spanish moss, and place appropriate representative materials at the respective places, Queen Elizabeth root at the pubic region for a female for instance.
People also sometimes use figurine candles, and treat them in a similar way.
But the most important part is the baptism, which is where you make the doll-baby the person it represents.