Its cylinder shape. But not sure one what level of thicknesz for cardboard
Answer from Piñata Boy
You want to use thin, single-layer cardboard like cereal box cardboard. You can get this in big sheets (as large as 3′ x 4′) for free at Sam’s or Costco. Just go to the stacks of paper towel and toilet paper, and the stacks are separated by these big sheets. They recycle them, so they’re happy to let you take them off their hands. See the Working With Cardboard page for a photo of what these cardboard sheets look like.
You’ll want to curl the sheet around to form a cylinder, but the thin cardboard won’t hold its shape as a piñata unless you stiffen it up with a layer or two of papier mâché. When you apply wet papier mâché to thin cardboard, the cardboard absorbs moisture and can start to warp, so it’s best if you can find something sturdy to wrap the thin cardboard around during the papier mâché work. You might want to tape two sheets together to get a Nerf bullet as large as the one in the photo.
Thin cardboard is hard to break as a piñata, so after stiffening up the cardboard with papier mâché you’ll probably want to punch holes in it to weaken the piñata. One other thing is that because this is a long, horizontal piñata, you might consider using two hanging hooks, each installed about 1/3 of the way in from opposite ends of the piñata. With only one hook it’s easy for the piñata to hang crooked or even vertically if all the candy falls to one end.
Good luck!