Begin by laying a trash bag out flat. Trim off the sides and bottom so you’re left with two big rectangles of plastic. Cut each piece into an approximate square.
2) Fold the triangles twice
Fold one of the squares in half diagonally to form a triangle. Fold that triangle in half two more times. This is slippery stuff, so use a few pieces of tape to fasten the layers together. It will help hold the shape together when you’re cutting.