I think you mean an egg carton. On day 18 you put the eggs in the carton, big end up. I use the paper cartons. You can use styrofoam or plastic, but you must cut a hole in the bottom for air circulation. I just did my first hatch in the egg carton. The chicks hatched a lot faster, and the mess isnt as bad, because the eggshells and the goop stay in the carton.